Transcript Chapter 16: The Hierarchical and Network Data Models

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”
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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”
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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”
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Description of Data Base
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Figure 16-7
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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”
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Hierarchies
Figure 16-8
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DL/1 Data Manipulation
Commands
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Figure 16-11
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Chapter 16
CODASYL DBTG Model
• Conference on Data Systems
Languages Data Base Task Group
• CODASYL also developed standards
for COBOL
• Complex and Incohesive
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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”
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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”
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CODASYL DBTG Program/Data
View Relationships
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Figure 16-12
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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”
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CODASYL DBTG Record Types
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Figure 16-13
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Two-Owner
Record
in
Different
Sets
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Figure 16-18
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Summary of Set Characteristics
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Figure 16-19
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Chapter 16
CODASYL DBTG Data
Manipulation Language
• FIND, GET
• FIND, MODIFY
• FIND, ERASE
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