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1. Introduction to DBMS questions and answers graded A+
What is a DBMS A Database Management System is a software package designed to store and manage databases. What does a DBMS store? A very large, in... [Show More] tegrated collection of data. What does a DBMS model? A real-world enterprise. What information does a DBMS model? Entities (e.g., students, courses) Relationships (e.g., Madonna is taking CS564) • When would you store data in a DBMS instead of in operating system files and vice-versa? (Section 1.3) - A database application must stage large datasets between main memory and secondary storage (e.g., buffering, page-oriented access, 32-bit addressing, etc.) - DBMS has special code for different queries - DBMS must protect data from inconsistency due to multiple concurrent users - DBMS must support crash recovery - DBMS must have security and access control • What are the main benefits of using a DBMS to manage data in applications involving extensive data access? (Sections 1.1, 1.4) - Data Independence - Efficient Data Access - Data Integrity and Security - Data Administration - Concurrent Access and Crash Recovery - Reduced Application Development Time Why Study Databases? - Shift from computation to information (low end: scramble to webspace high end: scientific applications) - Datasets increasing in diversity and volume - DBMS encompasses most of CS (OS, languages, theory, AI, multimedia, logic) What is a data model? (Section 1.5) A collection of concepts for describing data. What is a schema? (Section 1.5) A description of a particular collection of data, using a given data model. What is the most widely used model of data today? (Section 1.5) The relational model of data What is the relational data model? (Section 1.5) Main concept: relation is a table with rows and columns) (Every relation has a schema which defines columns or fields) What is data independence and how does a DBMS support it? Applications insulated from how data is structured and stored. Logical data independence: Protection from changes in logical structure of data. Physical data independence: Protection from changes in physical structure of data. Data independence is achieved through use of the three levels of data abstraction. The conceptual schema describes stored data in terms of a data model. The physical schema specifies additional storage details. The external schema, allows data access to be customized and authorized at the level of individual users or groups. Explain the advantages of using a query language instead of custom programs to process data. (Section 1.6) A DBMS takes great care to evaluate queries as efficiently as possible. Indexes can be used to speed up many queries----in fact, a good choice of indexes for the underlying relations can speed up each query in the preceding list. A DBMS enables users to create, modify, and query data through a data manipulation language (DML). • What is a transaction? What guarantees does a DBMS offer with respect to transactions? (Section 1.7) The ACID Test Atomic - Atomicity requires that each transaction be "all or nothing" Consistency - The consistency property ensures that any transaction will bring the database from one valid state to another Isolation - The isolation property ensures that the concurrent execution of transactions results in a system state that would be obtained if transactions were executed serially Durability - Durability means that once a transaction has been committed, it will remain so, even in the event of power loss, crashes, or errors • What are locks in a DBMS, and why are they used? 1. Every object that is read or written by a transaction is first locked in shared or exclusive mode, respectively. Placing a lock on an object restricts its availability to other transactions and thereby affects performance. Suppose that the following locking protocol is followed: Every transaction begins by obtaining a shared lock on each data object that it needs to read and an exclusive lock on each data object that it needs to rnod~fy, then releases all its locks after completing all actions. Consider two transactions T1 and T2 such that T1 wants to modify a data object and T2 wants to read the same object. Intuitively, if T1's request for an exclusive lock on the object is granted first, T2 cannot proceed until T1 relea..':les this lock, because T2's request for a shared lock will not be granted by the DBMS until then. Thus, all of T1's actions will be completed before any of T2's actions are initiated. • Identify the main components in a DBMS and briefly explain what they do. (Section 1.8) http://ecomputernotes.com/fundamental/what-is-a-database/components-of-dbms http://www.scs.ryerson.ca/~mcarberr/cps610/Recap.pdf 1. File Manager manages the allocation space on disk storage and the data structures used to represent info stored on other media. In most applications (99.9%) the file is the central element. All applications are designed with the specific goal: generation and use of information. A typical file system layered architecture is the following (see also CPS510). User Program Sequential Indexed Random Lists Logical I/O Basic File System Structure Device Drivers (Disk,tape,etc) Controllers Actual Device 2. Buffer Manager among other tasks, it transfers blocks between disk (or other devices) and Main Memory (MM). A DMA (Direct Memory Access) is a form of I/O that controls the exchange of blocks between MM and a device. When a processor receives a request for a transfer of a block, it sends it to the DMA which transfers the block uninterrupted. 3. Query Parser translates statements in a query language, whether embedded or not, into a lower level language. (See RL language example from CPS510). This parser is also a strategy selector: i.e., finding the best and most efficient way (faster?) of executing the query. 4. Authorization and Integrity Manager checks for the authority of the users to access and modify info, as well as integrity constraints (keys, etc). 5. Recovery Manager ensures that the database is and remains in a consistent (sound) state after any kind of failure. 6. Concurrency Controller enforces Mutual Exclusion by ensuring that concurrent interactions with the data base proceed without conflict (deadlocks, etc). • Explain the different roles of database administrators, application programmers, and end users of a database. Who needs to know the most about database systems? (Section 1.9) The DBA is responsible for many critical tasks: • Design of the Conceptual and Physical Schemas: The DBA is responsible for interacting with the users of the system to understand what data is to be stored in the DBMS and how it is likely to be used. Based on this knowledge, the DBA must design the conceptual schema (decide what relations to store) and the physical schema (decide how to store them). The DBA may also design widely used portions of the external schema, although users probably augment this schema by creating additional views. • Security and Authorization: The DBA is responsible for ensuring that unauthorized data access is not permitted. In general, not everyone should be able to access all the data. In a relational DBMS, users can be granted permission to access only certain views and relations. For example, although you might allow students to find out course enrollments and who teaches a given course, you would not want students to see faculty salaries or each other's grade information. The DBA can enforce this policy by giving students permission to read only the Courseinfo view. • Data Availability and Recovery from Failures: The DBA must take steps to ensure that if the system fails, users can continue to access as much of the uncorrupted data as possible. The DBA must also work to restore the data to a consistent state. The DBMS provides software support for these functions, but the DBA is responsible for implementing procedures to back up the data periodically and maintain logs of system activity (to facilitate recovery from a crash). • Database Tuning: Users' needs are likely to evolve with time. The DBA is responsible for modifying the database, in particular the conceptual and physical schemas, to ensure adequate performance as requirements change. Database application programmers develop packages that facilitate data access for end users, who are usually not computer professionals, using the host or data languages and software tools that DBMS vendors provide. (Such tools include report writers, spreadsheets, statistical packages, and the like.) Application programs should ideally access data through the external schema. It is possible to write applications that access data at a lower level, but such applications would comprornise data independence. DBA's need to know the most about database systems Why would you choose a database system instead of simply storing data in operating system files? When would it make sense not to use a database system? - Data Independence - Efficient Data Access - Data Integrity and Security - Data Administration - Concurrent Access and Crash Recovery - Reduced Application Development Time A DBMS is a complex piece of software, optimized for certain kinds of workloads (e.g., answering complex queries or handling many concurrent requests), and its performance may not be adequate for certain specialized applications. Examples include applications with tight real-time constraints or just a few well-defined critical operations for which efficient custom code must be written. Another reason for not using a DBMS is that an application may need to manipulate the data in ways not supported by the query language. In such a situation, the abstract view of the data presented by the DBMS does not match the application's needs and actually gets in the way. As an example, relational databases do not support flexible analysis of text data (although vendors are now extending their products in this direction). What is logical data independence and why is it important? Logical data independence: Protection from changes in logical structure of data. It shields users from changes in the logical structure of the data, or changes in the choice of relations to be stored. Explain the difference between logical and physical data independence. Logical data independence: Protection from changes in logical structure of data. Physical data independence: Protection from changes in physical structure of data. Explain the difference between external, internal, and conceptual schemas. The external schema, allows data access to be customized and authorized at the level of individual users or groups. The conceptual schema describes stored data in terms of a data model. The physical schema specifies additional storage details. What are the responsibilities of a DBA? If we assume that the DBA is never interested in running his or her own queries, does the DBA still need to understand query optimization? Why? • Design of the Conceptual and Physical Schemas: The DBA is responsible for interacting with the users of the system to understand what data is to be stored in the DBMS and how it is likely to be used. Based on this knowledge, the DBA must design the conceptual schema (decide what relations to store) and the physical schema (decide how to store them). The DBA may also design widely used portions of the external schema, although users probably augment this schema by creating additional views. • Security and Authorization: The DBA is responsible for ensuring that unauthorized data access is not permitted. In general, not everyone should be able to access all the data. In a relational DBMS, users can be granted permission to access only certain views and relations. For example, although you might allow students to find out course enrollments and who teaches a given course, you would not want students to see faculty salaries or each other's grade information. The DBA can enforce this policy by giving students permission to read only the Courseinfo view. • Data Availability and Recovery from Failures: The DBA must take steps to ensure that if the system fails, users can continue to access as much of the uncorrupted data as possible. The DBA must also work to restore the data to a consistent state. The DBMS provides software support for these functions, but the DBA is responsible for implementing procedures to back up the data periodically and maintain logs of system activity (to facilitate recovery from a crash). • Database Tuning: Users' needs are likely to evolve with time. The DBA is responsible for modifying the database, in particular the conceptual and physical schemas, to ensure adequate performance as requirements change. Actually the DBA needs to understand query optimization even more than the people who are running the queries, because how fast the query returns a result directly correlates to the value of the database to the end user. In addition, query optimization is an entire subfield of databases, and can be very difficult to do correctly. (25 pts) Scrooge McNugget wants to store information (names, addresses, descriptions of embarrassing moments, etc.) about the many ducks on his payroll. Not surprisingly, the volume of data compels him to buy a database system. To save money, he wants to buy one with the fewest possible features, and he plans to run it as a stand-alone application on his PC clone. Of course, Scrooge does not plan to share his list with anyone. Indicate which of the following DBMS features Scrooge should pay for; in each case, also indicate why Scrooge should (or should not) pay for that feature in the system he buys. (a) A security facility is necessary because Scrooge does not plan to share his list with anyone else. Even though he is running it on his stand-alone PC, a rival duckster could break in and attempt to query his database. The databases security features would foil the intruder. (5 pts) (b) Concurrency control is not needed because only he uses the database.(5 pts) (c) Crash recovery is essential for any database; Scrooge would not want to lose his data if the power was interrupted while he was using the system.(5 pts) (d) A view mechanism is needed. Scrooge could use this to develop custom screens that he could conveniently bring up without writing long queries repeatedly.(5 pts) (e) A query language is necessary since Scrooge must be able to analyze the dark secrets of his victims. In particular, the query language is also used to de ne views. What is a transaction? An atomic sequence of database actions (reads/writes). Why does a DBMS interleave the actions of different transactions instead of executing transactions one after the other? The DBMS interleaves the actions of different transaction in order to ensure consistency, e.g., prevent a situation such as a check being cleared while an account balance is being computed. What must a user guarantee with respect to a transaction and database consistency? Ensuring that a transaction (run alone) preserves consistency is ultimately the user's responsibility! What should a DBMS guarantee with respect to concurrent execution of several transactions and database consistency'? Users can specify some simple integrity constraints on the data, and the DBMS will enforce these constraints. The ACID Test Atomic - Atomicity requires that each transaction be "all or nothing" Consistency - The consistency property ensures that any transaction will bring the database from one valid state to another Isolation - The isolation property ensures that the concurrent execution of transactions results in a system state that would be obtained if transactions were executed serially Durability - Durability means that once a transaction has been committed, it will remain so, even in the event of power loss, crashes, or errors [Show Less]
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functions of a DBMS questions and answers latest updated
Data dictionary management DBMS stores definitions of data elements and relationships (metadata) in a dictionary. DBMS looks up required data component st... [Show More] ructures and relationships. Changes automatically recorded in the dictionary. DBMS provides data abstraction and removes structural and data dependency. Data Storage Management DBMS creates and manages complex structures required for data storage Also stores related data entry forms, screen definitions, report definitions, etc. Performance tuning: activities that make the database perform more efficiently DBMS stores the database in multiple physical data files Data transformation and presentation DBMS transforms data entered to conform to required data structures DBMS transforms physically retrieved data to conform to user's logical expectations Security management DBMS creates a security system that enforces user security and data privacy Security rules determine which users can access the database, which items can be accessed, etc. Uses multiple "tools" to manage: Transaction log Access control / privileges table Multiuser access control Allows many (thousands) of users to access the same data at the same time while maintaining all the changes as they are made. DBMS uses sophisticated algorithms to ensure concurrent access does not affect integrity Enforces transaction management and concurrency control Backup and recovery management DBMS provides backup and data recovery to ensure data safety and integrity Recovery management deals with recovery of database after a failure Critical to preserving database's integrity Data integrity management DBMS promotes and enforces integrity rules Minimizes redundancy Maximizes consistency Data relationships stored in data dictionary used to enforce data integrity Integrity is especially important in transaction-oriented database systems Database access language and application programming interfaces DBMS provides access through a query language Query language is a nonprocedural language Structured Query Language (SQL) is the de facto query language Standard supported by majority of DBMS vendors Database communication interfaces Current DBMSs accept end-user requests via multiple different network environments Communications accomplished in several ways: End users generate answers to queries by filling in screen forms through Web browser DBMS automatically publishes predefined reports on a Web site DBMS connects to third-party systems to distribute information via e-mail [Show Less]
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Chapter 1- Database Systems questions and answers
Ad hoc query a "spur-of-the-moment" question. centralized database A database located at a single site. data Raw facts, that is, facts tha... [Show More] t have not yet been processed to reveal their meaning to the end user. data anomaly A data abnormality that exists when inconsistent changes to a database have been made. For example, an employee moves, but the address change is corrected in only one file and not across files in the database. data dependence A data condition in which the data representation and manipulation are dependent on the physical data storage characteristics data dictionary A DBMS component that stores metadata- data about data. Thus, it contains the data definition as well as its characteristics and relationships. It may also include data that are external to the DBMS. data inconsistency A condition in which different versions of the same data yield different results data independence A condition that exists when data access is unaffected by changes in the physical data storage characteristics data integrity In a relational database, refers to a condition in which the data in the database is in compliance with all entity and referential integrity constraints data management A process that focuses on data collection, storage, and retrieval. Common functions include addition, deletion, modification, and listing data processing (DP) specialist ... data quality A comprehensive approach to ensuring the accuracy, validity, and timeliness of data data redundancy A condition that exists when a data environment contains unnecessarily duplicated data data warehouse Bill Inmon- an integrated, subject-oriented, time-variant, nonvolatile collection of data that provides support for decision making database A shared, integrated computer structure that houses a collection of related data. It contains two types of data: end-user data (raw facts) and metadata. The metadata consist of data about data, that is, the data characteristics and relationships database design The process that yields the description of the database structure. The process determines the database components. It is the second phase of the Database Life Cycle database management system (DBMS) Refers to the collection of programs that manages the database structure and controls access to the data stored in the database database system An organization of components that defines and regulates the collection, storage, management, and use of data in a database environment desktop database A single-user database that runs on a personal computer distributed database A logically related database that is stored over two or more physically independent sites enterprise database The overall company data representation, which provides support for present and expected future needs Extensible Markup Language (XML) a metalanguage used to represent and manipulate data elements. Unlike others, it permits the manipulation of a document's data elements. It is designed to facilitate the exchange of structured documents such as orders and invoices over the Internet. field A character or group of characters (alphabetic or numeric) that defines a characteristic of a person, place, or thing. For example, a person's Social Security Number, address, telephone number, and bank balance file A named collection of related records information the result of processing raw data to reveal its meaning. It consists of transformed data and facilitates decision making. islands of information A term used in the old-style file system environment to refer to independent, often duplicated, and inconsistent data pools created and managed by different organizational departments knowledge The body of information and facts about a specific subject. It implies familiarity, awareness, and understanding of information as it applies to an environment. A key characteristic is that "new" can be derived from "old" logical data format The way in which a human being views data metadata Data about data, that is, data concerning data characteristics and relationships. multiuser database A database that supports multiple concurrent users operational database A database that is designed primarily to support a company's day to day operations. performance tuning Activities that make a database perform more efficiently in terms of storage and access speed physical data format The way in which a computer "sees" (stores) data production database The main database designed to keep track of the day to day operations of a company query A question or task asked by an end user of a database in the form of SQL code. A specific request for data manipulation issued by the end user or the application to the DBMS query language A nonprocedural language that is used y a DBMS to manipulate its data. An example is SQL. query result set The collection of data rows that are returned by a query record A collection of related (logically connected) fields semistructured data Data that have already been processed to some extent single-user database A database that supports only one user at a time [Show Less]
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DBMS CH1 Questions with complete top solutions
Define each of the following terms: a. data b. field c. record d. file A. Data- Raw facts, such as a telephone number, a birth date, a customer name, ... [Show More] and a year-to-date (YTD) sales value. Data has little meaning unless it has been organized in some logical manner B. Field- A character or group of characters (alphabetic or numeric) that has a specific meaning. A field is used to define and store data. C. Record - A logically connected set of one or more fields that describes a person, place, or thing. For example, the fields that constitute a record for a customer might consist of the customer's name, address, phone number, date of birth, credit limit, and unpaid balance. D. File- A collection of related records. For example, a file might contain data about the students currently enrolled at Gigantic University. What is data redundancy, and which characteristics of the file system can lead to it? Data redundancy exists when the same data is stored unnecessarily at different places. The file system's structure makes it difficult to combine data from multiple sources. The organizational structure promotes the storage of the same basic data in different locations. The dispersion of data is exacerbated by the use of spreadsheets to store data. In a file system, the entire sales department would share access to the SALES data file through the data management and reporting programs created by the DP specialist. With the use of spreadsheets, each member of the sales department can create his or her own copy of the sales data. Because data stored in different locations will probably not be updated consistently, the islands of information often contain different versions of the same data. What is data independence, and why is it lacking in file systems? Data independence is a condition in which data access is unaffected by changes in the physical data storage characteristics. In a file system, making changes to an existing file structure requires multiple steps including: 1. Read a record from the original file 2. Transform the original data to conform to the new structure's storage requirements 3. Write the transformed data into the new file structure 4. Repeat the preceding steps for each record in the original file. Because all data access programs are subject to change when any of the file's data storage characteristics change (that is, changing the data type), the file system is said to exhibit data dependence. What is a DBMS, and what are its functions? A database management system (DBMS) is a collection of programs that manages the database structure and controls access to the data stored in the database. DBMS functions: 1. Data dictionary management: The DBMS uses the data dictionary to look up the required data component structures and relationships, thus relieving you from having to code such complex relationships in each program. Additionally, any changes made in a database structure are automatically recorded in the data dictionary, thereby freeing you from having to modify all of the programs that access the changed structure. In other words, the DBMS provides data abstraction, and it removes structural and data dependence from the system. 2. Data storage management: The DBMS creates and manages the complex structures required for data storage, thus relieving you from the difficult task of defining and programming the physical data characteristics. 3. Data transforming and presentation: The DBMS transforms entered data to conform to required data structures. The DBMS relieves you of the chore of distinguishing between the logical data format and the physical data format. That is, the DBMS formats the physically retrieved data to make it conform to the user's logical expectations. 4. Security management: The DBMS creates a security system that enforces user security and data privacy. 5. Multiuser access control: To provide data integrity and data consistency, the DBMS uses sophisticated algorithms to ensure that multiple users can access the database concurrently without compromising its integrity. 6. Backup and recovery management: The DBMS provides backup and data recovery to ensure data safety and integrity. 7. Data integrity management: The DBMS promotes and enforces integrity rules, thus minimizing data redundancy and maximizing data consistency. 8. Database access languages and application programming interfaces: The DBMS provides data access through a query language. Structured Query Language (SQL) is the de facto query language and data access standard supported by the majority of DBMS vendors. 9. Database communication interfaces: A current-generation DBMS accepts end- user requests via multiple, different network environments. What is structural independence, and why is it important? Structural independence exists when you can change the file structure without affecting the application's ability to access the data. What is the role of a DBMS, and what are its advantages? What are its disadvantages? DBMS roles: 1. Improved data sharing 2. Improved data security 3. Better data integration 4. Minimized data inconsistency 5. Improved data access 6. Improved decision making 7. Increased end-user productivity List and describe the different types of databases. 1. Single-user database: A database that supports only one user at a time 2. Multiuser database: A database that supports multiple concurrent users. 3. Desktop database: A single-user database that runs on a personal computer. 4. Workgroup database: A multiuser database that usually supports fewer than 50 users or is used for a specific department in an organization. 5. Enterprise database: Database that is used by the entire organization and supports many users (more than 50, usually hundreds) across many departments 6. Centralized database: A database located at a single site. 7. Distributed database: A logically related database that is stored in two or more physically independent sites. 8. Cloud database: A database that is created and maintained using cloud services, such as Microsoft Azure or Amazon AWS. 9. General-purpose database: A database that contains a wide variety of data used in multiple disciplines. 10. Discipline-specific database: A database that contains data focused on specific subject areas. 11. Operational database: A database designed primarily to support a company's day-to-day operations. 12. Analytical database: A database focused primarily on storing historical data and business metrics used for tactical or strategic decision making. What are the main components of a database system? 1. Hardware: Hardware refers to all of the system's physical devices, including computers (PCs, tablets, workstations, servers, and supercomputers), storage devices, printers, network devices (hubs, switches, routers, fiber optics), and other devices (automated teller machines, ID readers, and so on). 2. Software: Although the most readily identified software is the DBMS itself, three types of software are needed to make the database system function fully: operating system software, DBMS software, and application programs and utilities. 3. People: This component includes all users of the database system. On the basis of primary job functions, five types of users can be identified in a database system: system administrators, database administrators, database designers, system analysts and programmers, and end users. Each user type, described next, performs both unique and complementary functions. 4. Procedures: Procedures are the instructions and rules that govern the design and use of the database system. 5. Data: The word data covers the collection of facts stored in the database. Because data is the raw material from which information is generated, determining which data to enter into the database and how to organize that data is a vital part of the database designer's job. What is metadata? (data about data) The metadata describes the data characteristics and the set of relationships that links the data found within the database. For example, the metadata component stores information such as the name of each data element, the type of values (numeric, dates, or text) stored on each data element, and whether the data element can be left empty. The metadata provides information that complements and expands the value and use of the data. In short, metadata presents a more complete picture of the data in the database. Given the characteristics of metadata, you might hear a database described as a "collection of self-describing data." What are the potential costs of implementing a database system? 1. Increased costs 2. Management complexity 3. Maintaining currency 4. Vendor dependence 5. Frequent upgrade/replacement cycles Use examples to compare and contrast unstructured and structured data. Which type is more prevalent in a typical business environment? Unstructured data is data that exists in its original (raw) state—that is, in the format in which it was collected. Therefore, unstructured data exists in a format that does not lend itself to the processing that yields information. Structured data is the result of formatting unstructured data to facilitate storage, use, and the generation of information. You apply structure (format) based on the type of processing that you intend to perform on the data. Most data you encounter is best classified as semistructured. Semistructured data has already been processed to some extent. For example, if you look at a typical webpage, the data is presented in a prearranged format to convey some information. The database types mentioned thus far focus on the storage and management of highly structured data. [Show Less]
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Advantages of the DBMS questions and answers with complete top solutions
improved data sharing The DBMS helps create an environment in which end users have better access to more and better-managed data. Improved data sec... [Show More] urity The more users access the data, the greater the risks of data security breaches. A DBMS provides a framework for better enforcement of data privacy and security policies. Better data integration Wider access to well-managed data promotes an integrated view of the organization's operations and a clearer view of the big picture. Minimized data inconsistency The probability of data inconsistency is greatly reduced in a properly designed database. improved data access The DBMS makes it possible to produce quick answers to ad hoc queries. Improved decision making Better-managed data and improved data access make it possible to generare better-quality information, on which better decisions are based. increased end-user productivity The availability of data, combined with the tools that transform data into usable information, empowers end users to make quick, informed decisions that can make the difference between success and failure in the global economy. [Show Less]
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Chapter 1 - Database Management Systems, questions and answers latest updated
What is an entity? A person, place, object, event, or idea for which you want to store What is an attribute? A characteristic or property of an en... [Show More] tity What is an column or a field? Another name for attribute What is a Database Design? The process of determining the content and structure of data in a database in order to support some activity on behalf of a user or group of users What is a database? a structure that can store information about multiple types of entities, the attributes of those entities, and the relationships between the entities What is Entity-relationship (E-R) diagram? A visual way to represent a database. Rectangles represent entities, and lines represent relationships between connected entities What is redundancy? The duplication of data or the storing of the same data in more than one place What is a relationship? an association between entities What is a one-to-many relationship? The first entiy is associated with all of the occurances of the second entity, but the second entity is associated with only one of the occurance of the first entity What are the problems associated with redundancy? Difficulty accessing related data, limited security, size limitations, changes are cumbersome and time consuming, waste spaces, and leads to inconsistencies What is a data file? a file that are used to store data and the computer counterpart to an ordinary paper file. Spreadsheets, word-processors documents, and web pages are examples of it What is a Database Management system (DBMS) A program, or collection of programs, through which users interact with a database. Access, Oracle, DB2, MySQL, and SQL Server are examples of it What are Forms? A screen objects used to maintain, view, and print data from a database What are Reports? DBMS asks questions about the desired content and appearance of each report then creates it automatically based on the answers What is a primary key? A minimal collection of columns (attributes) in a table on which all columns are functionally dependent and that is chosen as the main direct-access vehicle to individual rows What is a record? A collection of related fields; can be thought of as a row in a table What is Data Independence? The property that lets you change the structure of a database without requiring you to change the programs that access the database; examples of these programs are the forms you use to interact with the database and the reports that provide information from the database. What is a Database Administration? The individual or group that is responsible for a database What is a Database Administrator? The individual who is responsible for a database, or the head of database administration. What is Integrity? A database has integrity if the data in it satis- fies all established integrity constraints What is Integrity constraint? A rule that must be followed by data in a database What is Security? The prevention of unauthorized access to a database [Show Less]
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DBMS - Database Management System, questions and answers
Database Collection of Data Management System a set of programs to store and retrieve data. DBMS (Database Management System) A collectio... [Show More] n of inter-related data that contains programs to store & access that data in an easy and effective manner. What is the need of DBMS? Store Data in an optimized and systematic manner and Retrieve Data Fast What are some Examples Applications where we use Database Management Systems are: Telecom Industry Banking Education sector Online shopping Advantages of DBMS over a FILE System no redundant data Data consistency and Integrity Secure Privacy Easy access to data Easy recovery Flexible Disadvantages of DBMS over FILE System Higher implementation Cost Complexity Performance for some applications What must you have to understand the view of data? Data Abstraction Instance and Schema What is data abstraction? The process of hiding irrelevant details from user What are the 3 levels of Data abstraction? Physical Logical View Physical abstraction level This is the lowest level of data abstraction. It describes how data is actually stored in database. You can get the complex data structure details at this level. records can be described as blocks of storage (bytes, gigabytes, terabytes etc.) in memory. Logical abstraction level - Middle level - Describes what data is stored in database - Developers and admins access this level. - records can be described as fields and attributes along with their data types, their relationship among each other can be logically implemented. View abstraction level - Highest level of data abstraction. - Describes the user interaction with database system. user just interact with system with the help of GUI and enter the details at the screen, they are not aware of how the data is stored and what data is stored; such details are hidden from them. Database Instance The data stored in database at a particular moment of time Database vs Instance Database is the set of files where application data (the reason for a database) and meta data is stored. An instance is the software (and memory) that Oracle uses to manipulate the data in the database. Database Schema Design of a database. Defines the variable declarations in tables that belong to a particular database; 3 Schema levels Physical Logical View keys in DBMS Used for identifying unique rows from table. Establishes relationship among tables. Types of keys Primary Super Candidate Alternate Composite Foreign Primary Key a column or set of columns in a table that uniquely identifies tuples (rows) in that table. -can not contain duplicate values or nulls Super Key a set ofone or more columns (attributes) to uniquely identify rows in a table. Candidate key minimal super keys with no redundant attributes. non-prime attribute An attribute that is not part of any candidate key prime attribute An attribute that is a part of one of the candidate keys is known as prime attribute. Super Key vs Candidate Key Candidate keys are selected from the set of super keys. they do not have any redundant attributes. That's the reason they are also termed as minimal super key. Foreign Key The columns of a table that points to the primary key of another table. They act as a cross-reference between tables. Foreign keys are the columns of a table that points to the candidate key of another table. Composite Key A key that consists of more than one attribute to uniquely identify rows in a table is called composite key. It is also known as compound key. Alternate key Out of all candidate keys, only one gets selected as primary key, remaining keys are known as alternative or secondary keys. Normalization a process of organizing the data in database to avoid data redundancy, insertion anomaly, update anomaly & deletion anomaly Anomalies problems that can occur in poorly planned, un-normalized databases where all the data is stored in one table 3 types of Anomalies in un-normalized db Insertion Update Delete Update anomaly Example: In a table we have two rows for an employee Rick as he belongs to two departments of the company. If we want to update the address of Rick then we have to update the same in two rows or the data will become inconsistent. If somehow, the correct address gets updated in one department but not in other then as per the database, Rick would be having two different addresses, which is not correct and would lead to inconsistent data. Insert anomaly Example: Suppose a new employee joins the company, who is under training and currently not assigned to any department then we would not be able to insert the data into the table if emp_dept field doesn't allow nulls. Delete anomaly Example: Suppose, if at a point of time the company closes the department D890 then deleting the rows that are having emp_dept as D890 would also delete the information of employee Maggie since she is assigned only to this department. How do you overcome anomalies? Normalize Data Common normal forms First normal form (1NF) Second normal form (2NF) Third normal form(3NF) Boyce & Codd normal form (BCNF) First normal form (1NF) an attribute (column) of a table cannot hold multiple values. It should hold only atomic values. a single row for each unique value Second normal form (2NF) Table is in 1NF (First normal form) No non-prime attribute is dependent on the proper subset of any candidate key of table. break column into a new table instead of having to update it twice if there is more then one record. Ie. add details table for age, height, etc. Third normal form(3NF) Table must be in 2NF Transitive functional dependency of non-prime attribute on any super key should be removed. Example of 3NF Break emp_zip, emp_state, emp_city and emp_district out of Employee table into Employee_Zip table so that they are not all dependent on employee_id. Then just have emp_zip in employee table Boyce & Codd normal form (BCNF) Advanced version of 3NF that's why it is also referred as 3.5NF. BCNF is stricter than 3NF. A table complies with BCNF if it is in 3NF and for every functional dependency X->Y, X should be the super key of the table. Transitive functional dependency each functional dependency X-> Y at least one of the following conditions hold: X is a super key of table Y is a prime attribute of table -can only occur in a relation of three of more attributes. Data Model A logical structure of Database that describes the design of database to reflect entities, attributes, relationship among data, constrains etc. Types of Data Models Object Based Record Based Object Based logical models Describe Data at the conceptual and view levels. E-R Model Object Oriented Model Physical Data Models describe data at the lowest level of abstraction. E-R Data Model (Entity-Relationship model) a systematic way of describing and defining a business process. An ER model is typically implemented as a database. The main components of E-R model are: entity set and relationship set. Record based logical Models describe data at the conceptual and view levels. These models specify logical structure of database with records, fields and attributes. Relational Model Hierarchical Model Network Model Relational Model The data and relationships are represented by collection of inter-related tables. Each table is a group of column and rows, where column represents attribute of an entity and rows represents records. [Show Less]
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Distributed Database Management Systems questions and answers 2023
Distributed Database Management System (DDBMS) Governs storage and processing of logically related data over interconnected computer systems Centra... [Show More] lized Database Management System Required that corporate data be stored in a single central site Distributed Processing Database's logical processing is shared among two or more physically independent sites via network Distributed Database Stores logically related database over two or more physically independent sites via computer network Database Fragments Database composed of many parts in distributed database system Transaction Processor (TP)(TM)(AP) Software component of a system that requests data Data processor (DP)(DM) Software component on a system that stores and retrieves data from its location Single-Site Processing, Single-Site Data (SPSD) Processing is done on a single host computer and data stored on host computer's local disk Mutliple-Site Processing, Single-Site Data (MPSD) Multiple processes run on different computers sharing a single data repository Mutliple-Site Processing, Multiple-Site Data (MPMD) Fully distributed database management system Homogeneous Integrate multiple instances of same DBMS over a network Heterogeneous Integrate different types of DBMSs Fully Heterogeneous Support different DBMSs, each supporting different data model Distribution Transparency Allows management of physically dispersed database as if centralized Transaction Transparency Ensures database transactions will maintain distributed database's integrity and consistency Two-Phase Commit Protocol (2PC) Guarantees if a portion of a transaction operation cannot be committed, all changes made at the other sites will be undone Performance Transparency Allows a DDBMS to perform as if it were a centralized database Failure Transparency Ensures system will operate in case of a network failure Network Latency Delay imposed by the amount of time required for a data packet to make a round trip Network Partitioning Delay imposed when nodes become suddenly unavailable due to a network failure CAP Consistency, Availability, Partition Tolerance [Show Less]
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Database Management System Chapter 1,questions and answers| A+ content
Database A collection of organized data that allows access, retrieval, and use of data. Database Management System (DBMS) Software through which u... [Show More] sers and application programs interact with a database Character Any written or printed letter, number, or symbol Field Group of related characters. Ex. Customer Name. Corresponds to Column in physical database Record a collection of fields about 1 customer (name, address, city, state, etc.) Corresponds to row in a physical database. File A group of records about the same type of entity (customers or inventory items) DBMS Functionality *Data Storage: Manage the physical structure of the database. *Security: control user access and privileges. *Multiuser access: Manage concurrent data access. *Backup: enable recovery options for database failures. *Data access language: provide a language that allows database access. *Data integrity: Enable constraints or checks on data. *Data dictionary: maintain information about database structure. Systems Development Life Cycle (SDLC) 1. Systems investigation: Understanding the problem 2. Systems analysis: Understanding the solution to the previously identified problem 3. Systems design: Defining the logical and physical components. 4. Systems implementation: Creating the system 5. Systems integration and testing: Placing the system into production. 6. Systems deployment: Placing the system into production. 7. Systems maintenance and review: Evaluating the implemented system. Entity Any person, place, or thing with characteristics or attributes that will be included in the system. Entity-Relationship Model (E-R Model) Used to depict the relationship that exists among entities E-R Model Relationships One-to-one One-to-many Many-to-many One-to-one Relationship Each occurrence of data in one entity is represented by only one occurrence of data in the other entity. Ex. Each individual has just one SSN and each SSN is assigned to just one person. One-to-many Relationship Each occurrence of data in one entity can be represented by many occurrences of the data in the other entity. Ex. A class has only one instructor, but each instructor can teach many classes. Many-to-many Relationship Data can have multiple occurrences in both entities. Ex. A student can take many classes, and each class is composed of many students. Cannot be included in the physical database. Database Normalization Determines required tables and columns for each table. Multistep process. Used to reduce or control data redundancy. Data redundancy When the same data exists in more than one place in a database. Data anomalies refers to data inconsistencies Unnormalized Data contains repeating groups in the Author column in the BOOKS table First-Normal Form (1NF) A relation that has a primary key and in which there are no repeating groups. Composite Primary Key More than one column is required to uniquely identify a row Can lead to partial dependency--a column is only dependent on a portion of the primary key. Second-Normal Form (2NF) The second stage in the normalization process in which a relation is in 1NF and there are no partial dependencies (dependencies in only part of the primary key). Third-Normal Form (3NF) level of normalization where it is 2NF and contains no transitive dependencies Relating tables within the database Once tables are normalized, make certain tables are linked. Tables are linked through a common field(existing in both tables). A common field is usually a primary key in one table and a foreign key("many" side of one-to-many) in the other table. Lookup Table Common description for the table referenced in a foreign key relationship. Structured Query Language (SQL) Data sublanguage Used to: Create or modify tables Add data to tables Edit data in tables Retrieve data from tables ANSI and ISO standards Primary Key A field (or group of fields) that uniquely identifies a given entity in a table Foreign Key A primary key of one table that appears as an attribute in another table and acts to provide a logical relationship between the two tables Common Field used to join data contained in two or more tables [Show Less]
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Database management systems (DBMS) questions and answers| latest updated
What is a database management system? a program controlling the structure of a database and access to the data; creates, processes, and administers databa... [Show More] se What are some advantages of a DBMS? -reduced data redundancy -improved data integrity -more program independence -increased user productivity -increased security What is DBMS used for? to create tables and relationships in databases What do applications use DBMS for? to read, insert, modify, and delete data What is a structured query language (SQL)? SQL is an international standard language for manipulating relational databases What do SQL queries consist of? an action, database table name, set of parameters What are SQL keywords? they issue instructions -create, delete, insert, etc. What are boo lean operators? AND, OR, NOT for searching What are global updates? based on some criteria What are joining tables? creating relationship What are some things that go into selecting a DBMS? database size number of concurrent users performance integration features vendor cost What is a database structure? an arrangement of the fields, tables, and relationships . . What are some techniques for creating a data model? entity relationship data model unified modeling language Database content? entities stored in database and relationship among those things What is an entity? item for which we want to store information -tables What is an attribute? specific piece of data about an entry -fields What is an entity relationship diagram (ERD)? picture of how data is related Are entities something that users want tracked? yes Entities may be... physical object logical construct transaction Entities are always... singular Entities have.. attributes: describe characters identifier: attribute whose value is associated with one and only on entity What is a database design? process of converting data model which transforms entities into tables and expresses relationships What is metadata? data that describes data makes data more useful makes data easier to use What is the most complex relationship? many-to-many What is a relational database design? designer creates table for every entity entity identifier becomes primary key of table attributes of entity become columns tables normalize to single theme represent relationships between table What is access? a relational database organized as a series of tables related through key fields What is a key field? field that is used to uniquely identify a record a key field.. allows for easier retrieval, analysis and manipulation of records What is a primary key? field that uniquely identifies each record What are objects? a table, forms, report, or query that can be created and manipulated as a unit by the user. What are tables in an access database? different groups of information -tables that are linked together to provide a related output What is a record in an access database? row in a table with information about one person, client, or other entity What is a field in an access database? smallest piece of information in a record, [Show Less]
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