1. CS370 Spring 2007 CS 370 Database Systems Lecture 1 Overview of Database Systems

2. CS370 Spring 2007 Questions in your mind… What is in this subject? Why we are studying this subject? What we shall get from this subject?

3. CS370 Spring 2007 Introduction to Databases Objectives: –What is Data and Information. –The characteristics of file-based systems. –The problems with the file-based approach. –The meaning of the term database. –The meaning of the term Database Management System (DBMS). –The typical functions of a DBMS. –The major components of the DBMS environment. –The problems involved in the DBMS environment. –The history of the development of DBMS. –The advantages and disadvantages of DBMS.

4. CS370 Spring 2007 Important Terms to Remember Database: organized collection of logically related data Data: stored representations of meaningful objects and events –Structured: numbers, text, dates –Unstructured: images, video, documents Information: data processed to increase knowledge in the person using the data Metadata: data that describes the properties and context of user data

5. CS370 Spring 2007 Data Management Example Suppose –You are a video store owner. –Customers rent video tape copies of movies. –Several copies of each movie. Needs –Which tapes has a customer rented? –Are any tapes overdue? –When will a tape become available?

6. CS370 Spring 2007 Solution: File – based System Edit rented.txt file Advantages –Text editors are easy to use –Simple to insert a record –Simple to delete a record

7. CS370 Spring 2007 Complications: Queries Does not address to needs Query: What movies has Ali Raza rented? Execute (not quite right): Search for ‘Ali Raza’. Query: Are any tapes overdue? Execute: ??? Requirements –Robust, sophisticated query language –Clear separation between data organization (schema) and data DBMS Concept DML SQL

8. CS370 Spring 2007 Complications: Multiple users Two clerks edit rented.txt file at the same time. –Ahmed starts to edit rented.txt, reads it into memory. –Sarah starts to edit rented.txt. –Ahmed adds a record. –Ahmed saves rented.txt to disk. –Sarah saves rented.txt to disk. Ahmed’s added record disappears! Requirements –Must support multiple readers and writers. –Updates to data must (appear to) occur in serial DBMS Concept Locks Concurrency control

9. CS370 Spring 2007 Complications: Crashes Crash during update may lead to inconsistent state. Some body makes 250 of 500 edits to change records Before he saves it, Windows crashes! Requirements –Must update on all or none basis. –Implemented by commit or rollback if necessary. DBMS Concepts Locks, Transactions Commit, Rollback Recovery

10. CS370 Spring 2007 Persistent storage Rented Tape file Inventory Master file Customer file Tape rental check in New tape ordering Customer info FILE-BASED SYSTEM

11. CS370 Spring 2007 Limitations of File – based Approach Separation and isolation of data –Each program maintains its own set of data. Users of one program may be unaware of potentially useful data held by other programs. Duplication of data –Same data is held by different programs. Wasted space and potentially different values and/or different formats for the same item. Data dependence –File structure is defined in the program code. Incompatible file formats –Programs are written in different languages, and so cannot easily access each others files.

12. CS370 Spring 2007 Database Approach Definition of data was embedded in application programs, rather than being stored separately and independently. No control over access and manipulation of data beyond that imposed by application programs. Result The database and Database Management System (DBMS)

13. CS370 Spring 2007 Database Approach INFORMATION –Information can be defines as data that has been organized in such a way as to be useful for someone or some use e.g. “A telephone directory is an information source” PROCESSING –It is the activity when a computer converts data into information. TYPES OF PROCESSING –Sorting, Searching, Filtering and Aggregating

14. CS370 Spring 2007 Database Approach SORTING –Recording data in a way so that it is easier to find data items. SEARCHING –Finding a particular data from among many(thousands even millions ) FILTERING –Selecting a smaller set of data items. AGGREGATING –Grouping, adding, counting etc of data items to produce a summary of the data.

15. CS370 Spring 2007 Sources of Data Data from orders placed by customers From public sources such as libraries Or more recently the Internet From commercial sources that provide specialised data such as mailing lists. CHARACTERISTIC OF USEFUL INFORMATION –It -- should be:- Up to date on time Relevant Complete Consistent Presented in a usable way and Secured against unauthorised access

16. CS370 Spring 2007 What is a Database? A database is a well-organized collection of data that are related in a meaningful way, which can be accessed in different logical orders but are stored only once. The data in the database is therefore integrated, structured, and shared. The main features of data in a database therefore are: –It is well organized –It is related –It is accessible in different orders without great difficulty –It is stored only once

17. CS370 Spring 2007 Database Users? Database administrators: –Responsible for authorizing access to the database, for coordinating and monitoring its use, acquiring software, and hardware resources, controlling its use and monitoring efficiency of operations Database Designers: –Responsible to define the content, the structure, the constraints, and functions or transactions against the database. They must communicate with the end-users and understand their needs End-users: –They use the data for queries, reports and some of them actually update the database

18. CS370 Spring 2007 Categories of End Users Casual: –Access database occasionally when needed Na ï ve or Parametric: –They make up a large section of the end-user population. They use previously well-defined functions in the form of “ canned transactions ” against the database. Examples are bank-tellers or reservation clerks who do this activity for an entire shift of operations. Sophisticated: –These include business analysts, scientists, engineers, others thoroughly familiar with the system capabilities. Many use tools in the form of software packages that work closely with the stored database. Stand-alone: –Mostly maintain personal databases using ready-to-use packaged applications. An example is a tax program user that creates his or her own internal database.