IMS DB Introduction to IMS Training Class 01 www. mainframes-online-training. weebly. com Polsani Anil Kumar
Introduction to Databases § § Data : Collection of facts suitable for communications Database is a collection of interrelated data items, stored once and organized in a form for easy retrieval. § Database Management System is a collection of programs for storing data, organizing, modifying and extracting data from a database. Database Structures Network Structures (e. g. IDMS) Hierarchical Structures (e. g. IMS DB) Relational Structures (e. g. DB 2)
File § § § Vs Databases Redundancy avoided Data insecure Security provided No control over data Field level sensitivity Threat to Integrity Consistency of data Lack of inbuilt Data Logging, recovery features § Data more redundant Checkpoint and Restart Lack of data Locks Automatic locks
Introduction to IMS § IBM’s Information Management System (IMS) , provides a hierarchical database management system for large MVS installations. There are two main components: § IMS/DB manages the data (Data Base) § IMS/DC provides a transaction processing system (Data Communications) IMS/DC is now known as IMS/TM (Transaction Manager).
History Of IMS § 1965 - Rockwell and IBM entered a partnership to develop an automated system to manage large bills of materials for the construction of a Spacecraft for man’s first trip to the moon. § 1966 - IBM started the design of ICS (Information Control System) and DL/I (Data Language I). Data Language-I (DL/I) was developed as a interface between application Program and data in IMS database. § DL/I Can interact with programming languages such as COBOL, PL/I. . § 1969 - ICS was renamed to IMS (Information Management System).
IMS Advantages § High Level Language support § Existing programs should not need modification due to database expansion or modification. § Data duplication avoided. § Provides Data security and integrity. § Recovery and reorganisation are easy. § CICS or IMS/DC provides the online access § Fast response with large data volumes
Hierarchical Databases Disadvantages § Retrieval logic depends on hierarchy § Cannot add children not having any parents § Dangerous to Update/delete parents having children
Types of Processing § On-line Processing (Message Processing Program. – MPP) § Batch Processing § Batch Message Processing program – (BMP) § DL/I Processing ONLINE MPP BATCH BMP DL/I
Types of Processing • BATCH DL/I • True batch processing • No data communication services are used • Databases accessed must be offline • MPP (Message Processing Program) • True online processing • Transaction are entered at terminal and stored in message queue • Databases accessed must be online
BATCH DL/I MPP AND BMP • BMP (Batch Message Processing) Two types 1. Transaction oriented: • Can read & write to online message queues • Can process online files and databases 2. Batch oriented: • Can only read message queues • Access online databases in batch mode
IMS Terminology Segment § Similar to a record § Contains one or more fields § Each grouping of data is called as a segment § Unit of data that Dl/I transfers to and from a program § in an I/O operation Segment type and occurrence are different
IMS Terminology § Root The segment at the top of the hierarchy on which all the other segment types depend. § Database Record All the segments which are related to one root segment. § Database A collection of database records.
IMS Terminology § Parent A segment which has a dependent segment § Child A segment which is dependent on another segment § Twins More than one occurrence of the same segment type under a single occurrence of the parent § Hierarchical Path The series of segments, starting at the root which have to be passed in order to access a particular segment.
IMS Terminology § Hierarchical Order The structure is always defined from Top-to-Bottom, Front-to. Back, Left-to-Right. § Hierarchical Level All segments at the same level in the structure § Search Field A named part of a segment known to IMS. Any number of fields may be named and used in processing. § Key Field The field used to determine the sequencing of twins under their parent. Multiple or unique key fields may be used.
IMS Terminology § Concatenated Key The key field values of the segments in an hierarchical path, placed side by side. § Current Position The starting position in the database; used by IMS to satisfy calls which are not directed elsewhere. § Parentage Position An established position at a specified segment which is treated as a parent (even though it might be at a higher level).
Database Structuring Rules § No limit to the number of database records § Each record may contain any number of segments within § There may be up to 255 different segment types § There is one root segment per database record § There may be any number of dependent segments per parent § A database record may have up to 15 hierarchical levels
Thank You Polsani Anil Kumar www. mainframes-online-training. weebly. com Polsani Anil Kumar
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