Database Management Systems TEXT BOOKS n 1

Database Management Systems

TEXT BOOKS n 1. Database Management Systems, Raghurama Krishnan, Johannes Gehrke, TATA Mc. Graw. Hill 3 rd edition n 2. Database System Concepts, Silberschatz, Korth, Mc. Graw hill, 5 th edition. n REFERENCES : n 1. Database Systems design, Implementation, and Management, Peter Rob & Carlos Coronel 7 th Edition. n 2. Fundamentals of Database Systems, Elmasri Navate, Pearson Education n 3. Introduction to Database Systems, C. J. Date, Pearson Education Database System Concepts 1. 2

Chapter 1: Introduction n Purpose of Database Systems n View of Data n Data Models n Data Definition Language n Data Manipulation Language n Transaction Management n Storage Management n Database Administrator n Database Users n Overall System Structure Database System Concepts 1. 3

Database Management System (DBMS) n Collection of interrelated data n Set of programs to access the data n DBMS contains information about a particular enterprise n DBMS provides an environment that is both convenient and efficient to use. n Database Applications: H Banking: all transactions H Airlines: reservations, schedules H Universities: registration, grades H Sales: customers, products, purchases H Manufacturing: production, inventory, orders, supply chain H Human resources: employee records, salaries, tax deductions n Databases touch all aspects of our lives Database System Concepts 1. 4

Some Issues n Creation of definitions/structures H Various views H Various types of users n Storing n Retrieving -- Indexes n Manipulating the data n Designing a good database --Normalization n Support for transactions H Crash recovery H Concurrent execution 4 Two clerks trying to reserve the same berth in a railway reservation system! 4 Two concurrent programs trying to add Rs 50 and Rs 100 to the same account. n Security Database System Concepts 1. 5

Purpose of Database System n In the early days, database applications were built on top of file systems n Drawbacks of using file systems to store data: H Data redundancy and inconsistency 4 Multiple file formats, duplication of information in different files H Difficulty in accessing data 4 Need to write a new program to carry out each new task H Data isolation — multiple files and formats. 4 It should be possible for you to write your program without worrying about other programs. Thinks that you alone is using the data. H Integrity problems 4 Integrity constraints (e. g. account balance > 0) become part of program code 4 Hard to add new constraints or change existing ones Database System Concepts 1. 6

Purpose of Database Systems (Cont. ) n Drawbacks of using file systems (cont. ) H Atomicity of updates 4 Failures may leave database in an inconsistent state with partial updates carried out 4 E. g. transfer of funds from one account to another should either complete or not happen at all H Concurrent access by multiple users 4 Concurrent accessed needed for performance 4 Uncontrolled concurrent accesses can lead to inconsistencies – E. g. two people reading a balance and updating it at the same time H Security problems n Database systems offer solutions to all the above problems Database System Concepts 1. 7

Levels of Abstraction n Physical level describes how a record (e. g. , customer) is stored. n Logical level: describes data stored in database, and the relationships among the data. H There are customers and accounts. Relationship is a customer can have one or many accounts. H Similarly a constraint saying that account-balance is non-negative is also part of the logical level description. n View level: There are several categories of users of a DBMS. They want to see the data in a particular form because of ease or clarity. Sometimes only part of a database is allowed to be accessed by a particular user. n There is only one Physical and Logical level schema, but there can be many view level schemas. Database System Concepts 1. 8

View of Data An architecture for a database system Database System Concepts 1. 9

Instances and Schemas n Similar to types and variables in programming languages n Schema – the description about the data -- Meta data (data about data) H Schema is also data ! H A program which wants to access data, should first access the schema to know the things likes format, type of the data, etc. H This is a powerful concept which allows us to see the data in a more abstract way. H Physical schema: database description at the physical level H Logical schema: database description at the logical level n Instance – the actual content of the database at a particular point in time H Analogous to the value of a variable n Physical Data Independence – the ability to modify the physical schema without changing the logical schema H Applications depend on the logical schema H 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. Database System Concepts 1. 10

Data Models n A collection of conceptual tools for describing data items along with relationship between them. It can also describe other information like constraints, etc. n Entity-Relationship model: A high level conceptual model which can be used to describe an enterprise without worrying about the technicalities of DBMS or any other system. H Good to do the requirements analysis. H Later on this can be converted easily into other models which are more technical. n Relational model: DB is a collection of relations. Relations(tables) are used to describe both data and relationships. n Other models: object-oriented model, semi-structured data models. Older models: network model and hierarchical model Database System Concepts 1. 11

Entity-Relationship Model An Example: ( we will see in detail later-on) Database System Concepts 1. 12

Entity Relationship Model (Cont. ) n E-R model of real world H Entities (objects) 4 E. g. customers, accounts, bank branch H Relationships between entities 4 E. g. Account A-101 is held by customer Johnson 4 Relationship set depositor associates customers with accounts n Widely used for database design at a very high abstract level H Database design in E-R model usually converted to design in the relational model (coming up next) which is used for storage and processing Database System Concepts 1. 13

Relational Model Attributes n Example of tabular data in the relational model Customer-id customername 192 -83 -7465 Johnson 019 -28 -3746 Smith 192 -83 -7465 Johnson 321 -12 -3123 Jones 019 -28 -3746 Smith Database System Concepts customerstreet customercity accountnumber Alma Palo Alto A-101 North Rye A-215 Alma Palo Alto A-201 Main Harrison A-217 North Rye A-201 1. 14

A Sample Relational Database System Concepts 1. 15

DDL and DML n Language for accessing and manipulating the data organized by the appropriate data model H DML also known as query language n Two classes of languages H Procedural – user specifies what data is required and how to get those data H Nonprocedural – user specifies what data is required without specifying how to get those data n SQL is the most widely used query language Database System Concepts 1. 16

DDL and DML : SQL n Data definition language is used to define schema (mostly at logical level) of a relation. H E. g. create table account ( account-number balance char(10), integer) n DDL compiler generates a table (relation) called account which is ready to be populated. n To insert a row (a data item) into the account table H insert into account values (‘A-9732’, 1200) Database System Concepts 1. 17

SQL n SQL: widely used non-procedural language which contains both DDL and DML. H E. g. find the name of the customer with customer-id 192 -83 -7465 select customer-name from customer where customer-id = ‘ 192 -83 -7465’ H E. g. 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-number n Application programs generally access databases through one of H Language extensions to allow embedded SQL H Application program interface (e. g. ODBC/JDBC) which allow SQL queries to be sent to a database Database System Concepts 1. 18

Database Users n Users are differentiated by the way they expect to interact with the system n Application programmers – Write applications which uses a database. They should know regarding how to access the database by using a host language, etc. n Sophisticated users – form requests in a database query language n Naïve users – Use already developed tools to access the data. E. g. people accessing database over the web, bank tellers, clerical staff Database System Concepts 1. 19

Database Administrator n Coordinates all the activities of the database system; the database administrator has a good understanding of the enterprise’s information resources and needs. n Database administrator's duties include: H Schema definition H Storage structure and access method definition H Schema and physical organization modification H Granting user authority to access the database H Specifying integrity constraints H Acting as liaison with users H Monitoring performance and responding to changes in requirements Database System Concepts 1. 20

Transaction Management n A transaction is a collection of operations that performs a single logical function in a database application n 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. n Concurrency-control manager controls the interaction among the concurrent transactions, to ensure the consistency of the database. Database System Concepts 1. 21

Storage Management n 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. n The storage manager is responsible to the following tasks: H interaction with the file manager H efficient storing, retrieving and updating of data Database System Concepts 1. 22

Overall System Structure Database System Concepts 1. 23

Application Architectures §Two-tier architecture: E. g. client programs using ODBC/JDBC to communicate with a database §Three-tier architecture: E. g. web-based applications, and applications built using “middleware” Database System Concepts 1. 24

History n It is closely related to the history of storage mediums from punched cards to hard disks; also related to data models from early network or hierarchical model to object oriented models. n 1950 s and early 1960 s: Magnetic tapes, punched cards are used as input medium. Output could be tape or punched card or printer. H Tapes are sequential, often main memory size is for lesser than the tape size. You need to write restricted programs which process at a time only a small quantity of data. n Late 1960 s and 1970 s: Hard disks. Random access. Allowed data structures to be stored on a disk. Network and hierarchical model of early databases is possible because of this. H A landmark paper by Codd [1970] defined the relational model and non-procedural ways of querying data in the relational model. H Codd won the prestigious Association of Computing Machinery Turing Award. Database System Concepts 1. 25

History n 1980 s: Hierarchical and network models dominated in late 1970 s, even though relational model is academically insteresting. H This is because, hierarchical and network models are efficient (speed) than relational models H Situation changed with System R, a ground breaking project at IBM Research that developed techniques for construction of an efficient relational database system. H Initial commercial RDBMS came into picture: IBM DB 2, Oracle, Ingres, and DEC Rdb H 1980 s saw much research on parallel and distributed databases, as well as initial work on object-oriented databases. Database System Concepts 1. 26

History n Early 1990 s: Transaction processing capabilities H Tools for analyzing large amounts of data n Late 1990 s: World Wide Web H High transaction processing rates H 24 X 7 working systems – no downtime even for maintenance. n Early 2000 s: H XML, XQuery new database technology. H Data warehousing, data mining tools Database System Concepts 1. 27