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Transcript
DATABASE By Mr. Abdalla A. Shaame 1 What is a database? The main characters of a database system The basic database design method The entity-relationship data model for application modeling 2 Types of databases • traditional • multimedia - pictures, video, sound • Scientific database - GIS: maps, weather, satellite images - biological database: DNA sequence analysis • warehouse, OLAP - analysis, decision making • real-time, active databases - industrial processes • deductive databases - combination of inference and databases 3 Database • collection of related data • represents some aspect of the real world • built with a specific purpose in mind • could be anywhere - notebook, spreadsheet, Access, Oracle, … could be manual / could be computerized Data • known and recordable facts • name, phone number, address, grade, ... 4 A database system is composed of four components; Data Hardware Software Users 5 6 Database Management System (DBMS) • collection of software facilitating the definition, construction and manipulation of databases Definition •record structure •data elements •names •data types •constraints etc Construction •create database files •populate the database with records Manipulation •querying •updating 7 Database Management System (DBMS) • collection of software facilitating the definition, construction and manipulation of databases DBMS Meta data Request manager Users/ actors Storage manager Stored database 8 Sample database file2 file1 Course CName CNo CrHrs Dept Database 8803 3 CS C 2606 3 CS Student Name StNo Class Major Smith 17 1 CS Brown 8 2 CS Grades StNo Sid Grade 17 25 A 17 43 B Section SId CNo Semester Yr Instructor 32 8803 Spring 2000 Smith 25 8803 Winter 2000 Smith 43 2606 Spring 2000 Jones file3 file4 9 Characteristics of the Database approach • single repository of data • sharable by multiple users •concurrency control •transaction control • self-describing - system catalogue contains meta data • program-data independence • some changes to the database are transparent to programs/users • multiple views of data - to support individual needs of programs/users 10 Database Actors • Database Administrator (DBA) - authorizing access to the database coordinating and monitoring its use aquiring software and hardware as needed solving problems such as breach of security or poor system performance • Database Designers/Modelers - identifying the data to be stored choosing appropriate data structure • End-users - access to the database: querying, updating, generating reports • Software Engineers - developing application programs 11 Advantages of the Database approach (capabilities we would look for in a DBMS) • controlled redundancy • database design integrates different user data needs • performance tuning may lead to replicated data • Sharing of the data • controlled/authorized access to data • Ensure integrity of the data • backup and recovery 12 Implications of the Database approach • standards enforcement • DBA can enforce standard naming conventions, etc • reduced application development time • adding new functionality to an existing database is “easy” • flexibility • adding new data and making some types of changes is “easy” • up-to-date information - due to sharable characteristic • economies of scale - due to sharable resources the whole organization can make one investment 13 When not to use a DBMS • overhead costs are too great • high initial investment • data and applications are simple, well-defined, not expected to change • stringent real-time constraints • multi-user environment not needed 14 Database design • let’s jump ahead to see this Course 1 Student Delivery M N Grades Section N 15 Database design • let’s jump ahead to see this Course StNo Class 1 Student Major Delivery Name M N Grades Section N 16 Database design • let’s jump ahead to see this CNo CrHrs Dept Course StNo Class CName 1 Student Major Delivery Name M N Grades Section N 17 Database design • let’s jump ahead to see this CNo CrHrs Dept Course StNo Class CName 1 Student Major Delivery Name M N Grades Semester Section N Year SId Instructor 18 Database design • let’s jump ahead to see this CNo CrHrs Dept Course StNo Class CName 1 Student Major Delivery Name M N Grades Semester Section N grade Year SId Instructor 19 name number With attributes, etc: fname name ssn bdate degree 1 lname minit sex startdate employee supervisor department works for N salary address 1 location 1 1 controls manages 1 N hours N supervisee number of employees N M 1 works on supervision dependents of project name number location N dependent name sex birthdate relationship 20 ER-to-Relational mapping 1. Create a relation for each strong entity type 2. Create a relation for each weak entity type • include primary key of owner (an FK - foreign key) • owner’s PK + partial key becomes PK 3. For each binary 1:1 relationship choose an entity and include the other’s PK in it as an FK. Include any attributes of the relationship 4. For each binary 1:n relationship, choose the n-side entity and include an FK of the other entity. Include any attributes of the relationship 21 5. For each binary M:N relationship, create a relation for the relationship • include PKs of both participating entities and any attributes of the relationship • PK is the concatenation of the participating entity PKs 6. For each multivalued attribute create a new relation • include the PK attributes of the entity type • PK is the PK of the entity type and the multivalued attribute 7. For each n-ary relationship, create a relation for the relationship • include PKs of all participating entities and any attributes of the relationship • PK may be the concatenation of the participating entity PKs 22