Chapter 1 HW 1A 1 1 Define the following terms data database DBMS database system database catalog program data independence user view DBA end user canned transaction deductive database system persistent object meta data and transaction processing application data Collection of known facts that can be recorded and have an implicit meaning database Collection of data DBMS It is a software that enables users to create and maintain a database It helps in defining constructing manipulating and sharing databases between different users and applications database system The DBMS software together with the data itself sometimes the applications database catalog Metadata such as definitions of database objects such as base tables views are also included and other functions are stored program data independence It is a property of DBMS access programs that allows a change in structure of some file independently from access programs by storing the structure of data files in the DBMS catalog separately from the access programs user view A view may be a subset of the database or it may contain virtual data that is derived from the database files but is not explicitly stored Each user may see a different view of the database which describes only the data of interest to that user DBA Database Administrator A person who is responsible for maintenance of a database environment by directing or performing all related activities to keep the data secure End user User who accesses the database for querying updating and generating reports End user is the primary reason for the creation of a certain database canned transaction Standard types of queries and updates which are frequently used by Naive end users to constantly querying and updating databases deductive database system Database systems which provide capabilities for defining deduction rules for inferencing new information from the stored database facts persistent object Survives the termination of program execution and can later be directly retrieved by another program Meta data Data that describes other data transaction processing application Application which allows several users at the same time to update the same data in a controlled manner so that the result of the updates is correct Discuss the main characteristics of the database approach and how it differs from traditional 1 3 file systems characteristics traditional file systems database approach Self describing nature of a database system In the file system approach each user defines and implements the needed files for a specific application to run File system doesn t contain any metadata Data abstraction No such data model is present in file system A DBMS catalog stores the description of a particular database e g data structures types and constraints The description is called meta data this allows the DBMS software to work with different database application A data model is a type of data abstraction that is used to hide storage details and present the users with a conceptual view of the database Program data independence Support multiple views of the data Sharing of data and multi user transaction processing The structures of data files is embedded in the access programs so many change to the structure of a file may require changing all programs that access this file DBMS access programs do not require such changes in most cases the structure of data files is stored in the DBMS catalog separately from the access programs If any changes are made to the structure of the files it will affect all the programs so changes to the structure of a file may require changing of all programs that access the file A view may be a subset of the database or it may contain virtual data that is derived from the database files but is not explicitly stored Cresting files over a long period leads to a possibility of information getting duplicated this redundancy is storing the same data multiple times leads to higher costs and wastage of space This may result in data inconsistency in the application this is because update is done to some of the files only and not all the files Allowing a set of concurrent users to retrieve from and to update the database concurrency control within the DBMS guarantees that each transaction is correctly executed or aborted Recovery subsystem ensures each completed transaction has its effect permanently recorded in the database 1 6 Discuss the capabilities that should be provided by a DBMS Backup and recovery DBMS s backup and recovery subsystem is responsible for recovery Enforce Integrity constraints DBMS should provide capabilities for defining and enforcing integrity constraints for the data Database designers should identify integrity constraints during the database design DBMS should act differently for different types of constraints Some of them can be specified to the DBMS and automatically enforced Some must be checked by update programs It can also happen that a data item is entered erroneously and still satisfies integrity constraints Restricting access DBMS should provide a security and authorization subsystem which the DBA uses to create accounts and to specify account restrictions The DBMS should enforce these restrictions automatically Control redundancy Normalization Redundancy in storing the same data multiple times could lead to several problems There is a duplication of effort storage space is wasted and files that represent the same data may become inconsistent Data normalization in the database approach ensures consistency and saves storage space However in practice it is sometimes necessary to use controlled redundancy to improve the performance of queries denormalization DBMS should have the capability to control any redundancy in order to avoid inconsistencies among the files Persistent storage for program objects A complex object in C or Java can be stored permanently in an object oriented DBMS That object is persistent since it exists after the termination of program execution and it can be retrieved later by another program Object oriented DBMS typically offer data structure compatibility with one or more object oriented programming languages Storage structures for efficient query processing To speed up disk search for the desired records DBMS often uses indexes They are based on tree data structures or hash data that are modified for disk search To obtain database records which we are querying those records must be copied from the disk to main