Lecture On Introduction (DBMS) By- Jesmin Akhter Assistant Professor, IIT, Jahangirnagar University

Database Approach Shared collection of logically related data (and a description of this data), designed to meet the information needs of an organization. The description of data is known as System Catalog, or Data Dictionary, or Meta Data. Is a Single, large repository of data which can be used simultaneously by many users. Provides advantages over file system management approach –Eliminates inconsistency, data anomalies, data dependency, and structural dependency problems –Stores data structures, relationships, and access paths Payroll System Tax Data Project Management System Personnel Data Projects Data 2 Prepared by Jesmin Akhter, Assistant Professor, IIT,JU

Main Characteristics of the Database Approach  Self-describing nature of a database system: A DBMS catalog stores the description of the database. The description is called meta-data. This allows the DBMS software to work with different databases.  Insulation between programs and data: Called program-data independence. Allows changing data storage structures and operations without having to change the DBMS access programs.  Data Abstraction: A data model is used to hide storage details and present the users with a conceptual view of the database.  Support of multiple views of the data: Each user may see a different view of the database, which describes only the data of interest to that user.  Sharing of data and multiuser transaction processing : allowing a set of concurrent users to retrieve and to update the database. Concurrency control within the DBMS guarantees that each transaction is correctly executed or completely aborted. OLTP (Online Transaction Processing) is a major part of database applications.  OLTP is used to refer to processing in which the system responds immediately to user requests. An automated teller machine (ATM) for a bank is an example of a commercial transaction processing application. 3

Prepared by Jesmin Akhter, Assistant Professor, IIT,JU Advantages of Using the Database Approach  Controlling redundancy in data storage and in development and maintenance efforts.  Sharing of data among multiple users.  Restricting unauthorized access to data.  Providing persistent storage for program  Providing Storage Structures for efficient Query Processing  Providing backup and recovery services.  Providing multiple interfaces to different classes of users.  Representing complex relationships among data.  Enforcing integrity constraints on the database.  Drawing Inferences and Actions using rules. 4

Database Management Database is shared, integrated computer structure housing: –End user data –Metadata Database Management System (DBMS) –Manages Database structure –Controls access to data –Contains query language Definition: A Database Management System (DBMS) is a software that enables users to define, create, and maintain the database. Prepared by Jesmin Akhter, Assistant Professor, IIT,JU

Importance of DBMS Makes data management more efficient and effective Query language allows quick answers to ad hoc queries Provides better access to more and better-managed data Promotes integrated view of organization’s operations Reduces the probability of inconsistent data 6 Prepared by Jesmin Akhter, Assistant Professor, IIT,JU

DBMS Manages Interaction Figure Prepared by Jesmin Akhter, Assistant Professor, IIT,JU

DBMS Functions Data dictionary management Data storage management Data transformation and presentation Security management Multiuser access control Backup and recovery management Data integrity management Database language and application programming interfaces Database communication interfaces 8 Prepared by Jesmin Akhter, Assistant Professor, IIT,JU

The ANSI-SPARC Architecture, where ANSI-SPARC stands for American National Standards Institute, Standards Planning And Requirements Committee, is an abstract design standard for a Database Management System (DBMS) The objective of the three-level architecture is to separate the users’ view(s) of the database from the way that it is physically represented. This is desirable since: –It allows independent customized user views: Each user should be able to access the same data, but have a different customized view of the data. These should be independent: changes to one view should not affect others. –It hides the physical storage details from users: Users should not have to deal with physical database storage details. They should be allowed to work with the data itself, without concern for how it is physically stored. Prepared by Jesmin Akhter, Assistant Professor, IIT,JU 9 Objective of the ANSI-SPARC Three-Level Architecture

–The database administrator should be able to change the database storage structures without affecting the users’ views. –The internal structure of the database should be unaffected by changes to the physical aspects of the storage: For example, a changeover to a new disk. –The database administrator should be able to change the conceptual or global structure of the database without affecting the users: This should be possible while still maintaining the desired individual users’ views. Prepared by Jesmin Akhter, Assistant Professor, IIT,JU 10 Objective of the ANSI-SPARC Three-Level Architecture

ANSI-SPARC Three-Level Architecture External Level –The users view of the database. Conceptual Level –The community view of the database Internal Level –Physical representation of the database on the computer. –Describes how the data is stored in the database. Prepared by Jesmin Akhter, Assistant Professor, IIT,JU

External level (View) –A view mechanism: Provides users with only the data they want or need to use. Reduce complexity; Provide a level of security; Provide a mechanism to customize the appearance of the database; Present a consistent, unchanging picture of the structure of the database, even if the underlying database is changed. Prepared by Jesmin Akhter, Assistant Professor, IIT,JU

ANSI-SPARC Three-Level Architecture Prepared by Jesmin Akhter, Assistant Professor, IIT,JU

This is the level of database architecture which contains –the definition of all the data to be stored in the database –rules and information about that structure and type of that data. The conceptual view is the complete description of the data stored in the database. It stores the complete data of the organization that is why it is also known as the community view of the database. The conceptual view shows all the entities existing in the organization, attribute or characteristics associated with those entities and the relationships which exist among the entities of the organization. Prepared by Jesmin Akhter, Assistant Professor, IIT,JU 14 Conceptual or Logical View

ANSI-SPARC Objectives: Two Types of Data Independence: –Logical Data Independence Refers to immunity of external schemas to changes in conceptual schema. Conceptual schema changes (add/remove), should not require changes to external schema or rewrites of application programs. –Physical Data Independence Refers to immunity of conceptual schema to changes in the internal schema. Internal schema changes (e.g. using different file organizations, storage structures/devices), should not require change to conceptual or external schemas. Prepared by Jesmin Akhter, Assistant Professor, IIT,JU

Multi User DBMS Architectures File-server –File-server is connected to several workstations across a network. Client-server –Server holds the database and the DBMS. Prepared by Jesmin Akhter, Assistant Professor, IIT,JU

File-Server Database resides on file-server. DBMS and applications run on each workstation. Disadvantages include: –Significant network traffic. –Copy of DBMS on each workstation. –Concurrency, recovery and integrity control more complex. Prepared by Jesmin Akhter, Assistant Professor, IIT,JU

Client-Server Architecture Client manages user interface and runs applications. Advantages include: –wider access to existing databases; –increased performance; –possible reduction in hardware costs; –reduction in communication costs; –increased consistency. Prepared by Jesmin Akhter, Assistant Professor, IIT,JU

Transaction Processing Monitor as middle tier of a three-tier client-server architecture Program that controls data transfer between clients and servers in order to provide a consistent environment, particularly for Online Transaction Processing (OLTP). Prepared by Jesmin Akhter, Assistant Professor, IIT,JU