2 2 2 Data Independence Classification of DBMS

● ﻟﻠﻘﺮﺍﺀﺓ 2. 2. 2. Data Independence

Classification of DBMS : ﻋﻠﻲ ﺃﺴﺎﺱ DBMS ﺗﺼﻨﻒ ﺍﻟـ DBMS ( ﺍﻟﻤﺴﺘﺨﺪﻡ ﻓﻲ ﺍﻟـ Data Model) ﻧﻤﻮﺫﺝ ﺍﻟﺒﻴﺎﻧﺎﺕ. 1 : (Main Criterion for Classification) Relational Data Model ﺍﻟﺤﺎﻟﻴﺔ ﺍﻣﺎ ﺗﺴﺘﺨﺪﻡ ﺍﻟـ DBMS ﻛﻞ ﺍﻟـ . Object Data Model ﺃﻮ Examples: Oracle, Access Relational DBMS IRIS, ORION Object DBMS Informix universal server: object-relational DBMS

2. ﻋﺪﺩ ﺍﻟﻤﺴﺘﺨﺪﻣﻴﻦ (Number of users supported by the system) ● DBMS ﺃﻤﺎ ﺍﻟـ ● ● Single user system (one user at the time using DB) ﺃﻮ Multiuser system (more than one user at a time concurrently) (Needs concurrency control)

3. ﻋﺪﺩ ﺍﻟـ sites ﺍﻟﺘﻲ ﻳﻤﻜﻦ ﺗﻮﺯﻳﻊ ﻗﺎﻋﺪﺓ ﺍﻟﺒﻴﺎﻧﺎﺕ ﻋﻠﻴﻬﺎ Number of Sites over which the database is distributed -: DBMS ﻫﻨﺎﻟﻚ ﻋﺪﺓ ﺃﻨﻮﺍﻉ ﻟﻠـ Sites ● ﻣﻦ ﺣﻴﺚ ﻋﺪﺩ ﺍﻟـ 1. Centralized DBMS (DB Stored at a single computer (site). Ex: - client – server module. DB Stored at the server 2. Distributed DBMS: DBMS Software and DB are distributed over many sites connected by computer network (homogeneous) 3. Federated DBMS (Multi database systems distributed across multiple sites , but each site user different DBMS (Heterogeneous DBMS)

4. Cost. 5. Type of access path options for storing files. 6. General purpose or specific purpose.

Good bye chapter TWO

Chapter (3) Data Modeling Using The Entity Relationship Model

ENTITY RELATIONSHIP MODEL ﻧﻤﻮﺫﺝ ﺍﻟﻜﺎﺋﻨﺎﺕ ﺍﻟﻤﺮﺗﺒﻄﺔ Popular high_ level conceptual data Model , developed by Peter Chen (1976). -: ﺍﻟﻤﻔﺎﻫﻴﻢ ﺍﻷﺴﺎﺳﻴﺔ ﻟﻠﻨﻤﻮﺫﺝ Entities ﺍﻟﻜﺎﺋﻨﺎﺕ. 1 Attributes ﺍﻟﺼﻔﺎﺕ. 2 Relationships ﺍﻟﻌﻼﻗﺎﺕ. 3

Entity Type name : Attributes: - employee Name, age , salary E 1 company Name, No, president C 1 Ali , 30000 Entity sets (extension) Sisco, ab 60, omer E 2 C 2 Ahmed, 40, 50000 ……. ……… Nilegroup, ac 360, ali ……. . . The collection of all entities of a particular entity type in the database at any point in time is called an entity set. Entity type & entity set have the same name.

ﺃﺸﻜﺎﻝ ﺍﻧﻮﺍﻉ ﺍﻟﺼﻔﺎﺕ Multivalued attribute: - Composite attribute : Sub parts attribute Composite attribute name

Derived Attribute : -

Value sets (Domain) ﻟﻬﺎ ﻣﺠﻤﻮﻋﺔ ﻣﻦ ﺍﻟﻘﻴﻢ ﺍﻟﺘﻲ ﻳﻤﻜﻦ ﺍﻥ ﺗﺎﺧﺬﻫﺎ ﺗﺴﻤﻰ E. T ﺃﻲ ﺻﻔﺔ ﻣﻦ ﺻﻔﺎﺕ ﺍﻝ . ( ﻟﻬﺬﻩ ﺍﻟﺼﻔﺔ Domain or Value sets ) ﺑﺎﻟﻤﺠﺎﻝ Value sets can’t be displayed In E-R diagram (Value sets (Domain ) + Key ) called attribute constraints in E-R model.