Introduction to Database Systems

1. Introduction to Database Systems Dr. Shafqat Ali Shad BSE(A,B)/MCS-1 2013

2. Course Goals This course is an introduction to the design, use, and internal workings of database management system. • Understanding Relational Model/Algebra: data is represented as a set of two dimensional tables and operators are defined by manipulate the data. • Database design: how to build a real database for real application? • Mastering SQL programming : you will master the operations on a database system. • Database System Implementation: Storage/Indexing/Transactions

3. References Database Systems: Principles, Design and Implementation by Catherine. M. Ricardo, (Mcmillan Publishing Company) Fundamentals of Database Systems by R. Elmasriand S. Navathe,. 3rd Edition 2000 Class notes

4. Prerequisites Data Structures Discrete Structures Structured Programming Language (C++) Software engineering topics related to project documentation and project design

5. Workload & Requirements Project (Individual) 2 Exams during the semester and Final Exam 2 Exams 25% of the final grade Final 35% of the final grade Quiz/ Assignments/ Attendance 25% Project 15% of the final grade No late projects will be accepted

6. Database Overview • File Management vs Database Management (why do we need database?) • Advantages of Database systems: storage persistence, programming interface, transaction management • Data Model (What is Data?) • Database Language (How to manipulate data?) • DBMS Architecture and Database System Components (like Oracle; mySQL) • Users classification (What kind of control you want over user transactions?)

7. Where are databases? You cannot avoid it and it’s everywhere! You can say it actually makes the current society and your life work! Banking/Credit card /Social Security Info… Online shopping/booking…

10. The DBMS Marketplace • Relational DBMS companies – Oracle, Sybase – are among the largest software companies in the world. • IBM offers its relational DB2 system. IBM is by some accounts the largest DBMS vendor in the world. • Microsoft offers SQL-Server, plus Microsoft Access for the cheap DBMS on the desktop. • OpenSource: mySQL, postgreSQL

11. Pre-Database Era: Stone Age of Data • Imagine you want build an online shopping website • Maintain products/categories (price, picture, properties, …) • Customers accounts • File is uninterpreted, unstructured collection of information • File operations: delete, catalog, create, rename, open, close, read, write, find, … • Access methods: Functions to implement operations along with internal file organization • Examples: File of Customers, File of Products; Access method: implementation of a set of operations on those files

12. C++ file programming open - open a file- specify how its opened (read/write) and type (binary/text) close - close an opened file read - read from a file write - write to a file seek - move a file pointer to somewhere in a file

13. File Management System Problems Any question (access) on the data is a small program!! Data redundancy Data is not isolated from the access implementation Multiple application (concurrent program) on the same file

14. Concurrent Program Execution Program1 AC=AC-50 AC #103 450 Program2 AC=AC-100 What is the final value of the account AC?

15. Security Problems Allow access to the file only to the authorized personnel Ability to restrict access to parts of the record Ability to control operation usage by different users Protection from unauthorized use Protection from the derivation of unauthorized information

16. Data Integrity • A database constraint is a logical constraint about the data expressed in a logical language. • STUDENT.AGE >15 • If (STUDENT.CLASS ==cse43005) then (STUDENT.PRIOR_CLASS ==cse31001) • Database is consistent if data at each time satisfies all integrity constraints. • Input to any application is a set of consistent data. An application output is a set of consistent data.

17. Collection of Files 60’s 70's 80's 90’s now Hierarchical Network Relational Choice for most new applications Object Bases Knowledge Bases

18. Advantages of Databases Persistent Storage – Database not only provides persistent storage but also efficient access to large amounts of data Programming Interface – Database allows users to access and modify data using powerful query language. It provides flexibility in data management Transaction Management – Database supports a concurrent access to the data

19. Early Database Applications Airline Reservation Systems – Data items are: single passenger reservations; Information about flights and airports; Information about ticket prices and tickets restrictions. Banking Systems – Data items are accounts, customers, loans, mortgages, balances, etc. Failures are not tolerable. Concurrent access must be provided Corporate Records – Data items are: sales, accounts, bill of materials records, employee and their dependents

20. Modern Database Applications • Client – Server architecture • DBMS serves as a server and client queries are sent to servers • Where to locate servers • Multimedia Applications • Multidatabase Applications • Data Warehouses • It’s everywhere!!

21. Three Aspects to Studying DBMS's 1. Modeling and design of databases. • Allows exploration of issues before committing to an implementation. 2. Programming: queries and DB operations like update. 3. DBMS implementation.

22. What Is Data ? • Different view points: • A sequence of characters stored in computer memory or storage • Interpreted sequence of characters stored in computer memory or storage • Interpreted set of objects • This maybe one of the most profound questions in computer science! It is still open and keep evolving!!

23. Data Levels and their Roles Physical – corresponds to the first view of data: How data is stored, how is it accessed, how data is modified, is data ordered, how data is allocated to computer memory and/or peripheral devices, how data items are actually represented (ASCI, EBCDIC,…) Conceptual – corresponds to the second view of data: What we want the data to express and what relationships between data we must express, what “ story” data tells, are all data necessary for the “story’ are discussed. View – corresponds to the third view of data:What part of the data is seen by a specific application

24. Physical Data - Example 10 3 6 10 3 6 RWP J 3 000375 0000035000 . . . . . . . . . Saqib 63 Physical

25. Examples • Conceptual • TA Name char(10), Age char (3), - Student Name char(10), Year-of_study char(3)

26. Examples A view - STUDENTS-TA Name char(25), Age char (3), Year-of_study char(3)

27. Three Level Data View –Data Abstractions . . . . . View1 View k Conceptual View Of Data Physical Data Storage

28. Logical Data Models • A collection of tools for describing • data • datarelationships • datasemantics • dataconstraints

29. A Break-through : Relational Model An enterprise is represented as a set of relations Domain – is a set of atomic values. Data type – Description of a form that domain values can be represented. Relation is a subset of a cartesian product of one or more domains The elements of relations are called tuples. Each element in the cartesian product is called attribute.

30. Relational Model Attributes Name City Student-id Street gpa Ali Faisal Rashid Usman Rizwan 192-83-7465 019-28-3746 192-83-7465 321-12-3123 019-28-3746 3.6 2.7 3.2 4.0 3.45 South North East North West ISB RWP WAH RWP ISB • Example of tabular data in the relational model

31. Object – Oriented Model An enterprise is described as a collection of objects and a collection of functions that work with objects Example: Person is an object. Object is characterized by a set of public attributes. Applications may refer only to public attributes; private attributes . Functions that implement the object may refer to private attributes; a set of protected attributes and a set of methods Attribute of an object can be another object Objects are nested into a hierarchy and can inherit attributes of their parents

32. Object Oriented Model OBJECT DATA MODEL 1. Complex Objects – Nested Structure (pointers or references) 2. Encapsulation, set of Methods/Access functions 3. Object Identity 4. Inheritance – Defining new classes like old classes

33. Example • Class Person{ public: Person(); ~Person(); float GetSalary(); float PutSalary(float&); string Name; int SSN; date BirthDate; private: float salary; }

34. Object-Oriented ModelData Encapsulation An object contains both data and methods to work with the data The physical data representation is visible only to the object creator. The implementation details of methods are not visible to object users An interface of the object consists of public attributes and methods Each object is characterized by an object identity

35. Data Manipulation Language • Language for accessing and manipulating the data organized by the appropriate data model • 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

36. Database Languages Department Faculty Dept Chair Name Dept SQL SELECT Chair FROM Faculty, DepartmentWHERE Faculty.name = “Nadir” AND Faculty.Dept = Department.Dept Data definition language (DDL) ~ like type definitions in C or C++ Data Manipulation Language (DML) Query (SELECT) UPDATE < relation name > SET <attribute> = < new-value> WHERE <condition>

37. Data Definition Language • Specification notation for defining the database schema • E.g. create tableaccount (account-numberchar(10),balanceinteger) • 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

38. Database Host Languages C, C++, Fortran, Lisp, COBOL Application prog. DBMS Calls to DB Local Vars (Memory) (Storage) Host language is completely general Query language—less general "non procedural" and optimizable

39. Database Definition A database is a collection of stored operational data used by various applications and/or users by some particular enterprise or by a set of outside authorized applications and authorized users A DataBase Management System (DBMS) is a software system that manages execution of users applications to access and modify database data so that the data security, data integrity, and data reliability is guaranteed for each application and each application is written with an assumption that it is the only application active in the database.

40. DBMS Architecture

41. Logical and Physical Database Components Logical Physical • Data Definition Language (DDL) • Data Manipulation Language (DML) • Host Language Interface • Data Administrator • Users • Query Processor • Compiler • Optimizer • Management • Transaction Manager • File Manager • Buffer Manager • Authorization and Integrity Manager

42. Query Processor Compiler – verifies whether a program or query is written in accordance with DDL and DML rules Optimizer – Finds the most effective way to access the required data and supply it in a user requested form. Monitors the query execution and modifies a query evaluation plan if necessary.

43. 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

44. Transaction Manager 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.

45. File Manager File Manager is responsible for mapping logical database units (objects, relations, etc.) into a set of low level files. It is responsible for maintenance of files and indexes on them. It should be able to create and destroy index and collect unused storage space to eliminate an unneeded gaps on disks.

46. Buffer Manager Buffer Manager is responsible for the allocation and maintenance buffer space in a memory to facilitate processing database data by several concurrent applications. Buffer Manager decides when to load data from a buffer to a database or discard the data and under what conditions a new data should be put into a buffer

47. Authorization and Integrity Manager This manager is responsible for granting an access to database or portions thereof only to authorized users and preventing the access to unauthorized users Integrity manager must assure data integrity during normal database operations as well as during the database failures

48. Data Administrator • 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

49. Database Users • Naïve – do not know about database too much, invoke application programs that are prepared already • Application Programmers – know how to interact with the system but may not know how DBMS is designed • Sophisticated users that know advanced use of the system and can use the system and packages on the top of the system • DBMS system users – write specialized database applications

50. A Little Design Methodology: Entity-Relationship Model The enterprise data can be described as a set of entities and a set of relationships between them. Entity – a data that pertains to, or describes some component of the enterprise Each entity is characterized by a set of attributes Relationship – describes an interconnection between different entities Entity Set – a set of entities that are characterized by the same entity definition Relationship Set – a set of relationships of the same type