Chapter A:Network Model Basic Concepts Data-Structure Diagrams The DBTG CODASYL Model DBTG Data-Retrieval Facility DBTG Update Facility DBTG Set-Processing Facility Mapping of Networks to Files Database System Concepts,5th Ed. A.1 @Silberschatz,Korth and Sudarshan
Database System Concepts, 5 A.1 ©Silberschatz, Korth and Sudarshan th Ed. Chapter A: Network Model Basic Concepts Data-Structure Diagrams The DBTG CODASYL Model DBTG Data-Retrieval Facility DBTG Update Facility DBTG Set-Processing Facility Mapping of Networks to Files
Basic Concepts Data are represented by collections of records. similar to an entity in the E-R model Records and their fields are represented as record type type customer record type account record customer-name:string; account-number:integer; customer-street:string; balance:integer; customer-city:string; end end Relationships among data are represented by links similar to a restricted(binary)form of an E-R relationship restrictions on links depend on whether the relationship is many- many,many-to-one,or one-to-one. Database System Concepts,5th Ed. A.2 ©Silberschat乜，Korth and Sudarshan
Database System Concepts, 5 A.2 ©Silberschatz, Korth and Sudarshan th Ed. Basic Concepts Data are represented by collections of records. similar to an entity in the E-R model Records and their fields are represented as record type type customer = record type account = record customer-name: string; account-number: integer; customer-street: string; balance: integer; customer-city: string; end end Relationships among data are represented by links similar to a restricted (binary) form of an E-R relationship restrictions on links depend on whether the relationship is manymany, many-to-one, or one-to-one
Data-Structure Diagrams Schema representing the design of a network database. A data-structure diagram consists of two basic components: Boxes,which correspond to record types. Lines,which correspond to links. Specifies the overall logical structure of the database. Database System Concepts,5th Ed. A.3 ©Silberschat乜，Korth and Sudarshan
Database System Concepts, 5 A.3 ©Silberschatz, Korth and Sudarshan th Ed. Data-Structure Diagrams Schema representing the design of a network database. A data-structure diagram consists of two basic components: Boxes, which correspond to record types. Lines, which correspond to links. Specifies the overall logical structure of the database
Data-Structure Diagrams(Cont.) For every E-R diagram,there is a corresponding data-structure diagram. customer-street account-number balance customer-name customer-city customer depositor account (a)E-R diagram customer-name customer-street customer-city account-number balance depositor customer account (b)Data structure diagram Database System Concepts,5th Ed. A.4 ©Silberschat乜，Korth and Sudarshan
Database System Concepts, 5 A.4 ©Silberschatz, Korth and Sudarshan th Ed. Data-Structure Diagrams (Cont.) For every E-R diagram, there is a corresponding data-structure diagram
Data-Structure Diagrams(Cont.) Since a link cannot contain any data value,represent an E-R relationship with attributes with a new record type and links. access-date customer-street Caccount-number balance customer-name customer-city customer depositor account (a)E-R diagram customer-name customer-street customer-city account-number balance customer account customer-date account-date access-date access-date (b)Network diagram Database System Concepts,5th Ed. A.5 @Silberschatz,Korth and Sudarshan
Database System Concepts, 5 A.5 ©Silberschatz, Korth and Sudarshan th Ed. Data-Structure Diagrams (Cont.) Since a link cannot contain any data value, represent an E-R relationship with attributes with a new record type and links