Composite

Key Characteristics

• • Multi-component Nature: Always consists of multiple individual parts, which together form a single logical unit.
  • Hierarchical Structure (COBOL): In COBOL, a GROUP item is a composite data item that contains other GROUP items or ELEMENTARY items, forming a hierarchy (e.g., 01 CUSTOMER-RECORD, 05 CUSTOMER-NAME, etc.).
  • Unique Identification (Databases): A composite key in DB2 or IMS is a primary or unique key made up of two or more columns (or fields in IMS) whose combined values uniquely identify a row or segment.
  • Optimized Access (Databases): A composite index is built on multiple columns, allowing the database manager to efficiently locate data based on criteria involving those columns.
  • Logical Grouping: Facilitates the organization of related data elements into a cohesive unit for processing or storage, improving data integrity and readability.

Use Cases

• • COBOL Record Definition: Defining a CUSTOMER-RECORD as a GROUP item composed of CUSTOMER-ID, CUSTOMER-NAME, and CUSTOMER-ADDRESS (which itself might be a GROUP item for street, city, state).
  • DB2 Primary Key: Creating a primary key for an ORDER_DETAIL table using a combination of ORDER_ID and ITEM_NUMBER to uniquely identify each line item within a specific order.
  • IMS Segment Key: Defining a unique key for a child segment (e.g., COURSE-ENROLLMENT) in an IMS database by concatenating fields from its parent STUDENT segment and its own COURSE-ID field.
  • DB2 Index for Query Optimization: Building a composite index on LAST_NAME and FIRST_NAME columns in an EMPLOYEE table to speed up queries that filter or sort by both names.

Related Concepts