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Database: A collection of related data [ Elmasri ] .

Database: A collection of related data [ Elmasri ] . A database represents some aspect of real world called “ miniworld ” [ Elmasri ] or “ enterprise ” [ Ramakrishnan ]. A database can be of any size and of varying complexity.

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Database: A collection of related data [ Elmasri ] .

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  1. Database: • A collection of related data [Elmasri]. • A database represents some aspect of real world called “miniworld” [Elmasri] or “enterprise”[Ramakrishnan]. • A database can be of any size and of varying complexity. • It may be generated and maintained manually or using computers.

  2. A few fundamental questions • What data to store? • How to describe this data? • How to store this data? • How to retrieve information from the data?

  3. Data Models • A data modelis a collection of concepts for describing data. • Aschemais a description of a particular collection of data, using a given data model. View 1 View 2 View 3 External Schema The three-schema architecture Conceptual Schema Conceptual Schema Physical Schema Internal Schema

  4. Example of Schemas in Relational Data Model • Conceptual schema: • Students (sid: string, name: string, login: string, • age: integer, gpa:real) • Courses (cid: string, cname:string, credits:integer) • Enrolled (sid:string, cid:string, grade:string) • Physical schema: • Relations stored as unordered files, heap files, or hashed files. • Index on first column of Students. Tree-based indexes or hash-based indexes can be used. • External Schema (View): • Course_info(cid:string,enrollment:integer)

  5. Classification of Databases By data model • Network Databases (early 1960s); E.g., IDS, IDMS • Hierarchical Databases (e.g., SABRE); E.g., IBM’s IMS • Relational (1970) Databases (RDBMS); widely used • Object-oriented Databases (OODBMS); E.g., ObjectStore, Poet. • Object-relational Databases (ORDBMS); • Deductive Databases • Active Databases • Real-time Databases • Spatial Databases • Temporal Databases • Multimedia Databases • Parallel and Distributed Databases

  6. Database Management System (DBMS): A software package designed to store and manage databases. Relational DBMSs: DB2, Informix, Oracle, Sybase, Microsoft Access, Microsoft SQL Server, FoxBase, Paradox, Teradata, MySQL, mSQL, etc.

  7. Advantage of DBMS: Data Independence • Applications insulated from how data is structured and stored • DBMS provides an abstract view, without exposing data representation and storage • DBMS also allow users to manipulate the data in a convenient way A1 P1 read/write OS vs. DMBS Data unit (file vs table) Data manipulation read/write DBMS OS .... : : 1100101010…

  8. Advantages of DBMS:Efficient Access • Use indexes • Sophisticate techniques are used to ensure efficient store and retrieval of massive data • Query optimization • rewrites query for a better response time using statistics maintained in the database management system • Support extremely large databases • Beyond the limitation of the underlying OS

  9. Advantages of DBMS:Reduce Application Development Time • Do not need to write the database management software for each application • Use standard query languages to access data such as SQL • Use standard ways to write database applications • JDBC for Java language • ODBC • Perl DBI • PHP • ProC

  10. Advantages of DBMS:Security & Integrity • Secrecy: Users should not be able to see things they are not supposed to. • E.g., A student can’t see other students’ grades. • Integrity: Users should not be able to modify things they are not supposed to. • E.g., Only instructors can assign grades. • Availability: Users should be able to see and modify things they are allowed to.

  11. Advantages of DBMS: Concurrency Control • Concurrent execution of user programs is essential for good DBMS performance. • Because disk accesses are frequent, and relatively slow, it is important to keep CPU working on several user programs concurrently. • Interleaving actions of different user programs can lead to inconsistency. • DBMS ensures such problems don’t arise: users can pretend they are using a single-user system.

  12. Query Optimization and Execution Relational Operators Files and Access Methods Buffer Management Disk Space Management DB Structure of a DBMS These layers must consider concurrency control and recovery • A typical DBMS has a layered architecture. • The figure does not show the concurrency control and recovery components. • This is one of several possible architectures; each system has its own variations.

  13. Career Choices in Database Areas • System analysts • Project managers • Database administrators • Database application developers/testers • Customer supports • Consultants • DBMS developers • Database Researchers • Database book authors • Database software instructors

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