Introduction to Advanced Database Systems Dr. Njogu

Source: IBM

Traditional File system  Drawbacks of using file systems to store data: Duplication of Data  Data redundancy and inconsistency- Duplication of Data Multiple file formats, duplication of information in different files Different systems/programs have separate copies of the same data  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

Traditional File system…  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

5 Traditional File system… Program-Data DependenceProgram-Data Dependence –All programs maintain metadata for each file they use Limited Data SharingLimited Data Sharing –No centralized control of data Lengthy Development TimesLengthy Development Times –Programmers must design their own file formats Excessive Program MaintenanceExcessive Program Maintenance –80% of of information systems budget

6 Problems with Data-Program Dependency Each application programmer must maintain their own dataEach application programmer must maintain their own data Each application program needs to include code for the metadata of each fileEach application program needs to include code for the metadata of each file Each application program must have its own processing routines for reading, inserting, updating and deleting dataEach application program must have its own processing routines for reading, inserting, updating and deleting data Lack of coordination and central controlLack of coordination and central control Non-standard file formatsNon-standard file formats

7 Three file processing systems at Pine Valley Furniture Duplicate Data

8 Problems with Data Redundancy Waste of space to have duplicate dataWaste of space to have duplicate data Causes more maintenance headachesCauses more maintenance headaches The biggest problem:The biggest problem: –When data changes in one file, could cause inconsistencies –Compromises data integrity

9 Solution: Database approach Central repository of shared dataCentral repository of shared data Data is managed by a controlling agentData is managed by a controlling agent Stored in a standardized, convenient formStored in a standardized, convenient form Requires a Database Management System (DBMS)

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…

The DBMS Marketplace Relational DBMS companies – Oracle, Sybase – are among the largest software companies in the world. IBM offers its relational DB2 system. With IMS, a nonrelational 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, answered by “lite” systems from other competitors. OpenSource: mySQL, postgreSQL

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: Algorithms 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

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

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

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!!

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.

Database Management System  A software system that is used to create, maintain, and provide controlled access to user databases.  DBMS manages data resources like an operating system manages hardware resources. 21

23

24 Elements of the Database Approach Components of the Database Environment Components of the Database Environment Enterprise Data ModelEnterprise Data Model –Graphical model showing high-level entities and relationships for the organization Relational Databases/DatabaseRelational Databases/Database –Database technology involving tables (relations) representing entities and primary/foreign keys representing relationships –Repository – centralized storehouse of metadata Use of Internet TechnologyUse of Internet Technology –Networks and telecommunications, distributed databases, client-server and 3- tier architectures Database ApplicationsDatabase Applications –Application programs used to perform database activities (create, read, update, and delete) for database users –Database Management System (DBMS) – software for managing the database

25 Elements of the Database Approach… CASE Tools – computer-aided software engineeringCASE Tools – computer-aided software engineering Data Administrators – personnel responsible for maintaining the databaseData Administrators – personnel responsible for maintaining the database System Developers – personnel responsible for designing databases and softwareSystem Developers – personnel responsible for designing databases and software End Users – people who use the applications and databasesEnd Users – people who use the applications and databases

26 Components of the database environment