Unit 01 dbms
- 1. DATABASE MANAGEMENT SYSTEMS MALLA REDDY ENGG. COLLEGE HYD II B. Tech CSE II Semester UNIT-I PPT SLIDES Text Books: (1) DBMS by Raghu Ramakrishnan (2) DBMS by Sudarshan and Korth
- 2. INDEX UNIT-1 PPT SLIDES S.NO Module as per Lecture PPT Session planner No Slide NO ------------------------------------------------------------------------------------------ 1. DBS Application and L1 L1- 1 to L1- 9 DBMS Vs File Systems 2. View of DATA L2 L2- 1 to L2- 7 3. DB Language (DML, DDL) L3 L3- 1 to L3- 6 4. DB Users and Administrator L4 L4- 1 to L4- 3 5. Data storage and Querying L5 L5- 1 to L5 -5 6. DBMS Architecture L6 L6- 1 to L6- 3
- 3. Database System Applications • DBMS contains information about a particular enterprise – Collection of interrelated data – Set of programs to access the data – 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 – Online retailers: order tracking, customized recommendations – Manufacturing: production, inventory, orders, supply chain – Human resources: employee records, salaries, tax deductions • Databases touch all aspects of our lives Slide No:L1-1
- 4. What Is a DBMS? • A very large, integrated collection of data. • Models real-world enterprise. – Entities (e.g., students, courses) – Relationships (e.g., Madonna is taking CS564) • A Database Management System (DBMS) is a software package designed to store and manage databases. Slide No:L1-2
- 5. Why Use a DBMS? • Data independence and efficient access. • Reduced application development time. • Data integrity and security. • Uniform data administration. • Concurrent access, recovery from crashes. Slide No:L1-3
- 6. Why Study Databases?? ? • Shift from computation to information – at the “low end”: scramble to webspace (a mess!) – at the “high end”: scientific applications • Datasets increasing in diversity and volume. – Digital libraries, interactive video, Human Genome project, EOS project – ... need for DBMS exploding • DBMS encompasses most of CS – OS, languages, theory, AI, multimedia, logic Slide No:L1-4
- 7. Files vs. DBMS • Application must stage large datasets between main memory and secondary storage (e.g., buffering, page-oriented access, 32-bit addressing, etc.) • Special code for different queries • Must protect data from inconsistency due to multiple concurrent users • Crash recovery • Security and access control Slide No:L1-5
- 8. Purpose of Database Systems • In the early days, database applications were built directly 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 “buried” in program code rather than being stated explicitly • Hard to add new constraints or change existing ones Slide No:L1-6
- 9. Purpose of Database Systems (Cont.) • Drawbacks of using file systems (cont.) – Atomicity of updates • Failures may leave database in an inconsistent state with partial updates carried out • Example: 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 – Example: Two people reading a balance and updating it at the same time – Security problems • Hard to provide user access to some, but not all, data • Database systems offer solutions to all the above problems Slide No:L1-7
- 10. Levels of Abstraction • Physical level: describes how a record (e.g., customer) is stored. • Logical level: describes data stored in database, and the relationships among the data. type customer = record customer_id : string; customer_name : string; customer_street : string; customer_city : string; end; • View level: application programs hide details of data types. Views can also hide information (such as an employee’s salary) for security purposes. Slide No:L1-8
- 11. Summary • DBMS used to maintain, query large datasets. • Benefits include recovery from system crashes, concurrent access, quick application development, data integrity and security. • Levels of abstraction give data independence. • A DBMS typically has a layered architecture. • DBAs hold responsible jobs and are well-paid! • DBMS R&D is one of the broadest, most exciting areas in CS. Slide No:L1-9
- 12. View of Data An architecture for a database system Slide No:L2-1
- 13. Instances and Schemas • Similar to types and variables in programming languages • Schema – the logical structure of the database – Example: The database consists of information about a set of customers and accounts and the relationship between them) – Analogous to type information of a variable in a program – Physical schema: database design at the physical level – Logical schema: database design at the logical level Slide No:L2-2
- 14. Instances and Schemas • Instance – the actual content of the database at a particular point in time – Analogous to the value of a variable • Physical Data Independence – the ability to modify the physical schema without changing the logical schema – Applications depend on the logical schema – In general, the interfaces between the various levels and components should be well defined so that changes in some parts do not seriously influence others. Slide No:L2-3
- 15. Data Models • A collection of tools for describing – Data – Data relationships – Data semantics – Data constraints • Relational model • Entity-Relationship data model (mainly for database design) • Object-based data models (Object-oriented and Object-relational) • Semi structured data model (XML) • Other older models: – Network model – Hierarchical model Slide No:L2-4
- 16. Data Models • A data model is a collection of concepts for describing data. • A schema is a description of a particular collection of data, using the a given data model. • The relational model of data is the most widely used model today. – Main concept: relation, basically a table with rows and columns. – Every relation has a schema, which describes the columns, or fields. Slide No:L2-5
- 17. 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) • Physical schema: – Relations stored as unordered files. – Index on first column of Students. • External Schema (View): – Course_info(cid:string,enrollment:integer) Slide No:L2-6
- 18. 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. One of the most important benefits of using a DBMS! Slide No:L2-7
- 19. DATA BASE LANGUAGE 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 – Declarative (nonprocedural) – user specifies what data is required without specifying how to get those data • SQL is the most widely used query language Slide No:L3-1
- 20. Data Definition Language (DDL) • Specification notation for defining the database schema Example: create table account ( account_number char(10), branch_name 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 • Specifies the storage structure and access methods used – Integrity constraints • Domain constraints • Referential integrity (e.g. branch_name must correspond to a valid branch in the branch table) – Authorization Slide No:L3-2
- 21. Relational Model • Example of tabular data in the Attributes relational model Slide No:L3-3
- 22. A Sample Relational Database Slide No:L3-4
- 23. SQL • SQL: widely used non-procedural language – Example: Find the name of the customer with customer-id 192-83-7465 select customer.customer_name from customer where customer.customer_id = ‘192-83-7465’ – Example: Find the balances of all accounts held by the customer with customer-id 192-83-7465 select account.balance from depositor, account where depositor.customer_id = ‘192-83-7465’ and depositor.account_number = account.account_number Slide No:L3-5
- 24. SQL • Application programs generally access databases through one of – Language extensions to allow embedded SQL – Application program interface (e.g., ODBC/JDBC) which allow SQL queries to be sent to a database Slide No:L3-6
- 25. Database Users 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 – Examples, people accessing database over the web, bank tellers, clerical staff Slide No:L4-1
- 26. Database Administrator • Coordinates all the activities of the database system – has a good understanding of the enterprise’s information resources and needs. • Database administrator's duties include: – Storage structure and access method definition – Schema and physical organization modification – Granting users authority to access the database – Backing up data – Monitoring performance and responding to changes • Database tuning Slide No:L4-2
- 27. Data storage and Querying • Storage management • Query processing • Transaction processing Slide No:L5-1
- 28. Storage Management • Storage manager is a program module that provides the interface between the low-level data stored in the database and the application programs and queries submitted to the system. • The storage manager is responsible to the following tasks: – Interaction with the file manager – Efficient storing, retrieving and updating of data • Issues: – Storage access – File organization – Indexing and hashing Slide No:L5-2
- 29. Query Processing 1.Parsing and translation 2. Optimization 3. Evaluation Slide No:L5-3
- 30. Query Processing (Cont.) • Alternative ways of evaluating a given query – Equivalent expressions – Different algorithms for each operation • Cost difference between a good and a bad way of evaluating a query can be enormous • Need to estimate the cost of operations – Depends critically on statistical information about relations which the database must maintain – Need to estimate statistics for intermediate results to compute cost of complex expressions Slide No:L5-4
- 31. Transaction Management • A transaction is a collection of operations that performs a single logical function in a database application • Transaction-management component ensures that the database remains in a consistent (correct) state despite system failures (e.g., power failures and operating system crashes) and transaction failures. • Concurrency-control manager controls the interaction among the concurrent transactions, to ensure the consistency of the database. Slide No:L5-5
- 32. Database Architecture The architecture of a database systems is greatly influenced by the underlying computer system on which the database is running: • Centralized • Client-server • Parallel (multiple processors and disks) • Distributed Slide No:L6-1
- 33. Overall System Structure Slide No:L6-2
- 34. Database Application Architectures (web browser) Old Modern Slide No:L6-3