E 4161 SISTEM KOMPUTER APLIKASI UNIT 13 REKABENTUK

E 4161 : SISTEM KOMPUTER & APLIKASI UNIT 13 – REKABENTUK MODEL PANGKALAN DATA RANGKAIAN

PANGKALAN DATA RANGKAIAN • Diperkenalkan sebagai penambahbaikan kepada model pangkalan data hierarki. • Set – hubungan antara rekod ahli dengan satu atau lebih bapa (pemilik). • Rekod – SALESREP, CUSTOMER, PRODUCT… • Pemilik – PRODUCT, INVOICE, PAYMENT…

PANGKALAN DATA RANGKAIAN • Ciri-ciri – Model rangkaian lebih fleksibel kerana maklumat boleh diperolehi melalui banyak cara. – Model rangkaian boleh mewakili jenis hubungan banyak ke banyak (M: M) – Setiap pemilik tidak terhad kepada hubungan satu arah sahaja dan setiap rekod boleh mempunyai lebih dari satu hubungan. – Setiap hubungan antara rekod ahli dan pemilik adalah melalui petunjuk.

PANGKALAN DATA RANGKAIAN • Struktur : – Rekod – Jenis rekod – Item data

PANGKALAN DATA RANGKAIAN • Jenis set – penerangan hubungan antara dua jenis rekod (1: M) • Jenis set mempunyai 3 elemen: – Nama untuk jenis set – Jenis rekod pemilik – Jenis rekod ahli

PANGKALAN DATA RANGKAIAN • Kejadian set – dibina oleh satu rekod pemilik dan beberapa rekod ahli dari jenis rekod ahli.

DATABASE MANAGEMENT SYSTEM BY R. PANNEERSELVAM • INSERTION IS AUTOMATIC – This means that if a member record is inserted in its record type, then it will be automatically connected to its associated owner record. One can use this type of insertion if the member records are to be permanently connected to their owner records for a longer period. • INSERTION IS MANUAL – This implies that if a member is inserted in its record type, then it will be connected to its associated owner record using an explicit program. This type of insertion can be used if the ownership of member records changes very often.

DATABASE MANAGEMENT SYSTEM BY R. PANNEERSELVAM • RETENTION means holding the association of member records with their respective owner records. • RETENTION IS FIXED – This means that the member records of a set are permanently associated with their owner records of that set. • RETENTION IS MANDATORY – The member records of a set are temporarily connected to their owner records of that set. This means that a given member record will keep changing its owner from time to time. – While changing the ownership of a member record, one can use any one of the following options: • DISCONNECT a member record from the present owner and then CONNECT it to a new owner. • RECONNECT the owner of a member record in single command.

DATABASE MANAGEMENT SYSTEM BY R. PANNEERSELVAM • RETENTION IS OPTIONAL – This type of retention permits the user to remove the association of owner records to their member records and leave its member records unconnected to some other owner records until told to do so by some user program. • ORDER • CHECK • SET SELECTION

LIBRARY DATABASE

SKIMA DDL

LIBRARY DATABASE publish set vchkout set checkout set T-A set collection set history set A-T set

SUBSKIMA DDL vchkout set checkout set collection set history set

DML • Retrieval commands: – FIND : used to locate a record in a given file of the database. – GET : used to transfer the content of the located record into the working area. – OBTAIN : an improved command to combine the functions of FIND and GET commands

DML • Modification commands: – STORE : include a new record into a database and connects it to all the sets in which the record is an automatic member. – MODIFY : update the contents of an existing record. – CONNECT : links a specific member record of a set which is currently located to its owner record. – DISCONNECT : delinks a currently located member record of a set from its owner record – RECONNECT : combines the function of DISCONNECT and CONNECT – ERASE : remove a record in a file of the database, disconnect it from its owner and remove all the records of member to which it is the owner.