The Data management component stores as well as retrieves sets of records. It implements the objects- set of records, network, cursor, record, field and view.
Records and fields:
A record type is a sequence of field types as well as a record instance is a corresponding sequence of field instances. Record types as well as instances are persistent objects. The record instances are the atomic units of insertion as well as retrieval. Fields are sub-objects of records as well as are the atomic units of update. Fields contain the attributes of atoms (example FIXED(31)or CHAR(*)) and field instances have atomic values (Example “3” or “BUTTERFLY”). Every record instance has a unique name called a record identifier (RID).
A field type constrains the type as well as values of instances of a field and defines the representation of such instances. The record type identifies what fields take place in instances of that record type.
A usual record might have ten fields and occupy 256 bytes although records often have hundreds of fields (example a record giving statistics on a census tract has over 600 fields), as well as may be very large (several thousand bytes). A extremely simple record (nine fields and about eighty characters) might be described by:
DECLARE 1 PHONE_BOOK_RECORD,2 PERSON_NAME CHAR(*),2 ADDRESS,3 STREET_NUMBER CHAR(*),3 STREET_NAME CHAR(*),3 CITY CHAR(*),3 STATE CHAR(*),3 ZIP_CODE CHAR(5).2 PHONE_NUMBER,3 AREA_CODE CHAR(3),3 PREFIX CHAR(3),3 STATION CHAR(4);
The operators on records comprises INSERT, DELETE, FETCH and UPDATE. Records are able to be CONNECTED to and DISCONNECTED from membership in a set (see below). These operators in actuality apply to cursors which in turn point to records.
The notions of record as well as field correspond very closely to the notions of record and element in COBOL or structure and field in PL/l. Records are variously denoted as entities, tuples, segments and rows by different subcultures. Most systems have alike notions of records although they may or mayn’t support optional fields (nulls), variable length fields or repeated fields.
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