The top-level dictionary object. Defines a logical view of a physical file — a collection of Elements grouped into a record. DCL is always required for MAGECIO to access any file. One DCL record exists per logical file (Data Class). The 3-character Data Class code becomes the prefix for all Element names and the Audit Stamp element name. 3-character Data Class code (e.g., CUS, ORD, INV) https://magec.com/DOC/db_main.htm#db004000 One per logical file 1 — Root Defines keys (primary and alternate/secondary) for a Data Class. The KYF definition is mandatory for all files; MAGEC will Abend with DB99 if it is missing. After a successful DCLADD, MAGEC automatically presents the KYFADD screen for the primary key. Multiple KYF records may exist per DCL (one per key). The DD Name (z/OS DD statement) linking the physical VSAM dataset to CICS is held here. Primary keys conventionally end in K1 (e.g., CUSK1). Data Class code + Key suffix (e.g., CUSK1, CUSK2) https://magec.com/DOC/db_main.htm#db005006 One-to-many per DCL (primary + optional alternates) 2 — Child of DCL Defines a logical grouping (portion) of a record — identified by a Displacement into the record and a Length. The Element is the smallest unit that MAGECIO can retrieve. ELT definitions are mandatory and must exist before DIT entries can be created. Element names are exactly 5 characters: first 3 = Data Class code, last 2 = element sequence (e.g., CUS01, CUS02). The Audit Stamp element is named DCLxx00 (e.g., CUS00) and is 36 bytes. 5-character Element name (Data Class code + 2-digit seq) https://magec.com/DOC/db_main.htm#db003002 One-to-many per DCL 2 — Child of DCL Defines individual fields (data items) within an Element. The Data Item is the MAGEC and COBOL equivalent of a "field." Each DIT record belongs to a specific ELT. DIT definitions drive automatic COBOL copybook generation, automatic screen editing, and Domain inheritance. DIT entries enable many automated MAGEC features including date editing, default value assignment, and DB2 host variable generation. Data Item name (COBOL dataname, prefixed by Data Class) https://magec.com/DOC/db_main.htm#db008000 One-to-many per ELT 3 — Child of ELT COBOL-source routines stored in the MAGEC library, associated with an ELT. A Business Rule is triggered (invoked by MAGECIO) whenever a program updates or adds data for the specified Element. Primary purpose is data integrity enforcement: cross-field and cross-file validations, assigning automatic key values, setting defaults, and cascading updates or deletes. Business Rules can reference screen fields via -IFEXIST control commands and include other copybooks via -MAGECINC. Library member name (naming convention driven by ELT name) https://magec.com/DOC/db_main.htm#db017001 Zero-to-many per ELT 3 — Child of ELT (sibling of DIT) A stored COBOL source-code definition generated from the DIT definitions of an Element. Copybooks are stored on the MAGEC library and are automatically included (expanded) by MMPCREAT and MBPCREAT into generated MMP and MBP programs via -MAGECINC statements. They define the Working Storage data layout for each Element and ensure data independence — programs are insensitive to physical record changes because they reference the dictionary-driven copybook, not hard-coded layouts. Both Element copybooks and Screen Mask copybooks exist. Library member name (derived from Element name) https://magec.com/DOC/db_main.htm#db007000 One per ELT (generated artifact) 3 — Child of ELT (sibling of DIT and Business Rules) One-to-Many Yes — KYF is mandatory for all files. DB99 abend occurs if missing when an MMP accesses the file. A Data Class (DCL) owns one or more Key definitions (KYF): at minimum the Master/Primary Key (e.g., CUSK1), and optionally one or more Alternate/Secondary Keys for browse functions. MAGEC automatically prompts for KYFADD immediately after a successful DCLADD. One-to-Many Yes — ELT definitions are mandatory and must exist before DIT entries can be defined. DB99 abend occurs if missing when an MMP accesses the file. A Data Class (DCL) contains one or more Elements (ELT). Each ELT defines a displacement and length window into the physical record. The first ELT is typically the 36-byte Audit Stamp (e.g., CUS00). One-to-Many Required to enable automated features (copybook generation, screen editing, DB2 host variable generation, domain inheritance, etc.). Each Element (ELT) contains one or more Data Items (DIT) — the individual COBOL fields. DIT entries must reference a valid ELT. They drive automatic copybook generation and automatic screen edit validation in generated MMP programs. One-to-Many (optional) No — Business Rules are optional. Zero or more may exist per ELT. Business Rules are associated with an ELT and are invoked by MAGECIO whenever data for that Element is added or updated. They enforce referential integrity, cross-field validations, and automatic key assignment. Stored as COBOL source members in the MAGEC library. One-to-One (generated) Generated artifact — produced by the MAGECLBR or MMPCREAT process from the DIT definitions belonging to the ELT. Each Element (ELT) produces one COBOL Copybook stored on the MAGEC library. The copybook is automatically included into every generated MMP or MBP that accesses the Element via -MAGECINC. This mechanism provides data independence: changing the physical record requires only regenerating the copybook, not recoding the programs. After any DCL, KYF, or ELT change, issue the LOAD Function Code in the SFUNCT field to reload MAGEC's main-memory dictionary tables without restarting CICS. Ref: https://magec.com/DOC/db_main.htm#db004002 DB99 abend occurs when an MMP attempts file access and the DCL, KYF, or ELT definition is missing from the dictionary. Ref: https://magec.com/DOC/markdown/01-ai-assistant-facts.md.txt DB93 abend occurs when an Element name or Key name is inconsistent with its owning Data Class code. Ref: https://magec.com/DOC/markdown/01-ai-assistant-facts.md.txt The diagram shows multiple KYF and ELT boxes stacked to indicate that multiple instances (primary + alternates for KYF; multiple Elements for ELT) are permitted under a single DCL. MAGECIO — not the application programs — handles all physical file I/O. Programs communicate via the Request Area in the TWA. The dictionary hierarchy (DCL → KYF + ELT → DIT) is what MAGECIO reads at runtime to service those I/O requests. Ref: https://magec.com/DOC/db_main.htm