The CA IDMS/DB Environment

 
idms
 
In CA IDMS/DB, the basic structure is the
set
. A set consists of
record types
that are related as
owner
and
member
. Individual record types can participate in more than one relationship (set) either as owner or member (that is, a member record type can have more than one owner record type).
Multiple Ownership Support
Support for multiple ownership is the most basic difference between DL/I and CA IDMS/DB. In DL/I, a child segment (equivalent to a member record type) can have one and only one parent segment (equivalent to an owner record type).
DL/I's support for bidirectional logical relationships provides the functional equivalent of multiple ownership.
2
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Schema The Top-Level Definition
In CA IDMS/DB, the top-level definition is known as the
schema
. The schema names all of the allowable record types and defines the
elements
(fields) that can appear in each record type. The schema also names and defines the possible relationships among the record types; these defined relationships are the sets.
Subschema The Second-Level Definition
The second-level definition in CA IDMS/DB is known as the
subschema
. As its name indicates, the subschema defines a subset of the top-level schema definition. (While a subschema is usually a subset of a schema, it can also duplicate a schema in its entirety.) Any number of subschemas can be defined for a given schema.
Defining CA IDMS/DB Databases
Use Data Description Language (DDL)
The database administrator prepares the schema definition using source statements provided in the
schema data description language
(Schema DDL). The database administrator codes the subschema definitions using similar source statements provided in the
subschema data description language
(Subschema DDL).
You use CA IDMS physical data definition language statements to create a DMCL module that maps the schema areas to physical files and defines buffers for database operations.
For more information on defining a DMCL, see the
CA IDMS Database Administration Section.
DDL Compilers Process Source Statements
Separate schema and subschema DDL compilers process the source statements. The CA IDMS Command Facility is used to produce assembler source for the DMCL module. The DMCL assembler source must then be assembled to produce object modules that map the logical areas into physical files and set up the necessary buffers.
Executing CA IDMS/DB Applications
At application run time, CA IDMS/DB loads the object-form subschemas and DMCL modules. The application is then ready to start issuing
data manipulation language
(DML) calls for database operations. The object-form subschemas serve as control tables for the application. These subschemas maintain status information so the application can check the results of database requests.
Basic CA IDMS/DB Components
CA IDMS/DB Components
The diagram below illustrates the basic components in the CA IDMS/DB environment.
For more information on complete descriptions of all of the CA IDMS/DB components, see the
CA IDMS Database Design Section
and
CA IDMS Database Administration Section
.
IDMSDB--Basic CA IDMS/DB Components