Database Processing Chapter 16 The Hierarchical and Network

Database Processing Chapter 16 The Hierarchical and Network Data Models David M. Kroenke © 2000 Prentice Hall

Chapter 16 DL/I “Language for processing a database, implemented in the hierarchical database, IMS (Information Management System) from IBM” Page 453 © 2000 Prentice Hall

Chapter 16 DL/I Hierarchical Terms • Field “smallest unit of data” • Segment “groups of fields; nodes of the tree structure” • Data base record “a collection of related segments; a particular tree structure” • Data base “composed of database records” Page 453 © 2000 Prentice Hall

Chapter 16 DL/I Hierarchical Terms • Data base description “how data base records are defined; set of assemblylanguage macro instructions” • Root “first segment” • Sequence field “one field in each segment used to order the occurrences of a given type” Page 453 © 2000 Prentice Hall

Description of Data Base Page 455 Figure 16 -7 © 2000 Prentice Hall

Chapter 16 DL/I Hierarchical Terms • Physical data base record (PDBR) “describes the data as it exists in data storage” • Logical data base record (LDBR) “describes the data as they appear to the application program” Page 457 © 2000 Prentice Hall

Hierarchies Figure 16 -8 Page 456 © 2000 Prentice Hall

DL/1 Data Manipulation Commands Page 462 Figure 16 -11 © 2000 Prentice Hall

Chapter 16 CODASYL DBTG Model • Conference on Data Systems Languages Data Base Task Group • CODASYL also developed standards for COBOL • Complex and Incohesive Page 462 © 2000 Prentice Hall

Chapter 16 CODASYL DBTG Terms • Schema “complete logical view of the database” • Subschema “view of the database as it appears to an application program” • Data structure description “maps schema records, fields, and relationships to physical storage” Page 462 © 2000 Prentice Hall

Chapter 16 CODASYL DBTG Terms • User working area “contains database and control data for a particular user” • Run-unit “the execution of a program by one of the users” Page 463 © 2000 Prentice Hall

CODASYL DBTG Program/Data View Relationships Page 463 Figure 16 -12 © 2000 Prentice Hall

Chapter 16 CODASYL DBTG Terms • Data-item “a field that corresponds to an attribute (column)” • Record “a collection of data-items” • Set “a one-to-many relationship” Page 463 © 2000 Prentice Hall

CODASYL DBTG Record Types Page 464 Figure 16 -13 © 2000 Prentice Hall

Two-Owner Record in Different Sets Page 466 Figure 16 -18 © 2000 Prentice Hall

Summary of Set Characteristics Page 467 Figure 16 -19 © 2000 Prentice Hall

Chapter 16 CODASYL DBTG Data Manipulation Language • FIND, GET • FIND, MODIFY • FIND, ERASE Page 470 © 2000 Prentice Hall