THE NETWORK DATA MODEL SECTION 8

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THE NETWORK DATA MODELSECTION 8

• An early DBMS

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Background

• Networks are a natural way of representing
  relationships among objects

• The network data model represents data in network
  structures of record types connected in
  one-to-one or one-to-many relationships

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• Conference on Data Systems Language

• Early 1960s

• American Standards Institute (ANSI) 1971
• IDS and IDMS

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Concepts

• Schema

• Subschema
• Physical details

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• Records and Sets

• Record type

• Set
• Owner record type
• Member record type

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A Bachman Diagram
A Data Structure Diagram
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Instance or Occurrence
An Example of a Network Data Structure
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• Types of Networks

• Simple networks

• Complex networks
• Link record type

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An Example of a Link Record
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Expanded Example
Converts a complex network into a simple network
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The Models Relationship to Conceptual Modeling
Semantics

• An example of a conceptual model?

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• RULE 1

• For each entity of set E in a conceptual schema,
  create a record type R in the network data
  structure. All attributes of E are represented as
  fields in R

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• Representing One-to-Many Relationships

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• Transforming n-ary Relationships

• An example could be a three-way relationship

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• Must create a link record

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• The Database from the above example

LINK 1
PRODUCTS
COUNTRIES
Australia
Widget
LINK 2
Canada
Clamp
LINK 3
USA
Gadget
LINK 4
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• Transforming Many-To-Many Relationships

• An manufacturer may produce many products, and
  any one of these products can be made by several
  manufacturers

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Data Definition Language

• What is the DDL?

• Use the DDL to define the database schema
• The following procedure should be used.

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• Procedure

• Create the conceptual data model

• Map the conceptual data model to network data
  structure diagrams
• Use the DDL to implement the schema

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• A schema is made up of

• Schema section

• Record sections
• Set sections

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1. Create the conceptual model

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1. Map to a network structure

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1. Implement the schema

1. SCHEMA NAME IS ACCOUNTSREC
2. RECORD NAME IS CUSTOMER
3. CUST-ID TYPE IS NUMERIC INTEGER
4. NAME TYPE IS CHARACTER 15
5. ADDRESS TYPE IS CHARACTER 20
6. ACCOUNT-BALANCE TYPE IS NUMERIC (5,2)
7. RECORD NAME IS INVOICE
8. INVONO TYPE IS NUMERIC INTEGER
9. DATE TYPE IS CHARACTER 9
10. AMOUNT TYPE IS NUMERIC (5,2)
11. STATUS TYPE IS CHARACTER 2
12. RECORD NAME IS LINE-ITEM
13. STOCKNO TYPE IS NUMERIC INTEGER
14. DESCRIPTION TYPE IS CHARACTER 20
15. PRICE TYPE IS NUMERIC (4,2)
16. CUSTINV

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• From Schema to Subschema

• Title division

• Mapping division
• Structure division
• Subschema record section
• Subschema set section

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• Subschema Example

• SS INVSTATUS WITHIN ACCOUNTSREC.
• MAPPING DIVISION.
• ALIAS SECTION.
• AD RECORD CUSTOMER IS OWEDBY.
• AD SET CUST-INV IS OWEDBY INV.
• STRUCTURE DIVISION.
• RECORD SECTION.
• 01 OWEDBY.
• 05 CUST-ID.
• 05 NAME.
• 05 ACCOUNT-BALANCE.
• 01 INVOICE ALL.
• SET SECTION.
• SD OWEDBY-INV

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Data Manipulation Language

• What is the DML?

• Process records one at a time
• The following procedure should be used.

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• Basic Commands

• Navigational commands

• Retrieval commands
• Update commands
• Records
• Sets

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• Basic DML Commands

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• Some terms defined

• User working area

• Currency indicators
• Status flags
• Record templates

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Relationship of User Working Area to Database
Instances
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• Retrieval and Update

• FIND Command

• GET Command

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• ERASE Command

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• MODIFY Command

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• STORE Command

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• Set Operations

• CONNECT Command

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• DISCONNECT Command

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• RECONNECT Command

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• Set Membership Classification

• Set insertion class

• Defined by the statement
• INSERTION IS ltinsert modegt
• Manual insertion or Automatic insertion

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• Manual Insertion Mode

• Must be placed by using CONNECT
• CONNECT ltrecord typegt TO ltset typegt

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• Automatic Insertion Mode

• Must be placed by using STORE
• STORE ltrecord typegt

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• Set Retention

• Retention options are
• Fixed
• Mandatory
• Optional

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Implementation

• Large size

• Well-defined repetitive queries
• Well-defined transactions
• Well-defined applications