DBMS introduction and functionality of of dbms
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Database management systems (DBMS) allow for the storage and manipulation of large collections of related data. A DBMS includes software that provides efficient access to data and ensures data integrity. Key benefits of DBMS include data independence, efficient data access, data integrity and security, concurrent access and crash recovery. DBMS touch many aspects of daily life through applications in banking, transportation, education and more.
DBMS introduction and functionality of of dbms
- 2. DATABASE
- 3. Database Systems: Then Database Systems: Today
- 5. Collection of interrelated data Set of programs to access the data DBMS contains information about a particular enterprise DBMS provides an environment that is both convenient and efficient to use. Database Applications: Banking: all transactions Airlines: reservations, schedules Universities: registration, grades Sales: customers, products, purchases Manufacturing: production, inventory, orders, supply chain Human resources: employee records, salaries, tax deductions Databases touch all aspects of our lives
- 6. DBMS components Hardware The physical computer system that allows physical access to data Software The actual program that allows users to access, maintain, and update physical data Data: stored physically on the storage devices User: include end users and application programs Procedure A set of procedures (rules) that should be clearly defined and followed by the users of the database
- 8. In the early days, database applications were built on top of file systems Drawbacks of using file systems to store data: *Data redundancy and inconsistency Multiple file formats, duplication of information in different files *Difficulty in accessing data Need to write a new program to carry out each new task *Data isolation — multiple files and formats * Integrity problems Integrity constraints (e.g. account balance > 0) become part of program code Hard to add new constraints or change existing ones
- 9. Drawbacks of using file systems (cont.) * Atomicity of updates Failures may leave database in an inconsistent state with partial updates carried out E.g. transfer of funds from one account to another should either complete or not happen at all * Concurrent access by multiple users Concurrent accessed needed for performance Uncontrolled concurrent accesses can lead to inconsistencies E.g. two people reading a balance and updating it at the same time * Security problems Database systems offer solutions to all the above problems
- 10. ARCHITECTURE
- 11. Physical Schema Conceptual Schema View 1 View 2 View 3 DB Users • Views describe how users see the data. • Conceptual schema defines logical structure • Physical schema describes the files and indexes used. • (sometimes called the ANSI/SPARC model)
- 12. Example: University Database • 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) • External Schema (View): – Course_info(cid:string,enrollment:integer) • Physical schema: – Relations stored as unordered files. – Index on first column of Students.
- 13. Instances and Schemas Similar to types and variables in programming languages Schema – the logical structure of the database (e.g., set of customers and accounts and the relationship between them) Instance – the actual content of the database at a particular point in time
- 14. Data Independence • 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. Physical Schema Conceptual Schema View 1 View 2 View 3 DB
- 15. DATABASE MODELS
- 16. • A collection of tools for describing: – Data – Data relationships – Data semantics – Data constraints • Object-based logical models – Entity-relationship model – Object-oriented model – Semantic model – Functional model • Record-based logical models – Relational model (e.g., SQL/DS, DB2) – Network model – Hierarchical model (e.g., IMS)
- 17. Entity-Relationship Model Example of entity-relationship model
- 18. E-R model of real world Entities (objects) E.g. customers, accounts, bank branch Relationships between entities E.g. Account A-101 is held by customer Johnson Relationship set depositor associates customers with accounts Widely used for database design Database design in E-R model usually converted to design in the relational model (coming up next) which is used for storage and processing
- 19. Relational Model
- 22. Data Languages
- 23. Data Definition Language (DDL) Specification notation for defining the database schema E.g. create table account ( account-number char(10), balance integer) DDL compiler generates a set of tables stored in a data dictionary Data dictionary contains metadata (i.e., data about data) database schema Data storage and definition language language in which the storage structure and access methods used by the database system are specified Usually an extension of the data definition language
- 24. Data Manipulation Language (DML) Language for accessing and manipulating the data organized by the appropriate data model DML also known as query language Two classes of languages Procedural – user specifies what data is required and how to get those data Nonprocedural – user specifies what data is required without specifying how to get those data SQL is the most widely used query language
- 25. Database User
- 26. Users are differentiated by the way they expect to interact with the system • Application programmers – interact with system through DML calls • Sophisticated users – form requests in a database query language • Specialized users – write specialized database applications that do not fit into the traditional data processing framework • Naïve users – invoke one of the permanent application programs that have been written previously E.g. people accessing database over the web, bank tellers, clerical staff
- 28. Coordinates all the activities of the database system; the database administrator has a good understanding of the enterprise’s information resources and needs. Database administrator's duties include: • Schema definition • Storage structure and access method definition • Schema and physical organization modification • Granting user authority to access the database • Specifying integrity constraints • Acting as liaison with users • Monitoring performance and responding to changes in requirements
- 29. Advantages of a DBMS
- 30. • Data independence • Efficient data access • Data integrity & security • Data administration • Concurrent access, crash recovery • Reduced application development time • So why not use them always? • Expensive/complicated to set up & maintain • This cost & complexity must be offset by need • General-purpose, not suited for special- purpose tasks (e.g. text search!)
- 31. Databases make these folks happy ... • DBMS vendors, programmers – Oracle, IBM, MS, Sybase, … • End users in many fields – Business, education, science, … • DB application programmers – Build enterprise applications on top of DBMSs – Build web services that run off DBMSs • Database administrators (DBAs) – Design logical/physical schemas – Handle security and authorization – Data availability, crash recovery – Database tuning as needs evolve
- 32. • DBMS used to maintain, query large datasets. – can manipulate data and exploit semantics • Other benefits include: – recovery from system crashes, – concurrent access, – quick application development, – data integrity and security. • Levels of abstraction provide data independence – Key when dapp/dt << dplatform/dt
- 33. • DBMS R&D represents a broad, fundamental branch of the science of computation • DBAs, DB developers the bedrock of the information economy