THE NETWORK DATA MODEL SECTION 8 An early DBMS. Background Networks are a natural way of representing relationships among objects The network data model.

THE NETWORK DATA MODEL

SECTION 8

An early DBMS

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

Conference on Data Systems Language

• Early 1960s

• American Standards Institute (ANSI) – 1971

• IDS and IDMS

Concepts

• Schema

• Subschema

• Physical details

Records and Sets

• Record type

• Set

• Owner record type

• Member record type

A Bachman Diagram A Data Structure Diagram

CUSTOMER

PURCHASE-ORDER

LINE-ITEMS

SALESPERSONOWNER OWNER

MEMBEROWNER

MEMBER

SALESPO SETCUSTPO SET

POITEM SET

One-to-many relationship

One-to-one relationship

Instance or Occurrence

Smith Jones Bean

PO #1 PO #2 PO #3 PO #4

Pens Pencils Erasers Envelopes

Darwin Wallace

CUSTOMER SALESPERSON

An Example of a Network Data Structure

Types of Networks

• Simple networks

• Complex networks

• Link record type

An Example of a Link Record

STUDENT

CLASS

Thus a complex network

STUDENT

STUDENT-ID

CLASS

CLASS-ID

TAKING CLASS SET

ENROLLED SET

SC

Expanded Example

Sue White Judy Dench

PB A461

Peter Black

PB E230 SW A461 SW E230 JD A461PB B304

Botany 304 English 230Accounting

461

Converts a complex network into a simple network

The Model’s Relationship to Conceptual Modeling Semantics• An example of a conceptual model?

CUSTOMER ACCOUNTHAS-

ACCOUNT1 N

CUST-ID NAME ADDRESS ACCT # BALANCE

CUST-ID NAME ADDRESS BALANCEACCT #CUSTOMER ACCOUNT

CUSTOMER/ACCOUNT SET

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

Representing One-to-Many Relationships

CUSTOMER ACCOUNT

CUSTOMER ACCOUNT

RULE 2For one-to-many relationships, the record type on the “one” side of the relationship becomes the owner, the record type on the “many” side becomes the member record type. If the relationship is strictly one-to-one, then the owner and member record types are chosen arbitrarily.

Transforming n-ary Relationships

•An example could be a three-way relationship

PRODUCT

DATE

COUNTRYSOLDN M

M

• Must create a link record

PRODUCT DATE COUNTRY

LINKRECORD

Product/Link Set

Date/Link Set Country/Link

Set

RULE 3For each n-ary relationships, n > 2, create a linking record L, and make it the member record type in n set types. Designate the owner of each set type as the record type on the “one” side of the resulting on-to-many relationship.

Nov. 2, 1999 Jan. 15, 2000Jan. 13 2000Dec. 5, 1999DATES

LINK 1

LINK 2

LINK 3

LINK 4

Australia

Canada

USA

Widget

Clamp

Gadget

PRODUCTS COUNTRIES

•The Database from the above example

Transforming Many-To-Many Relationships

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

MANUFACTURER PRODUCT

RULE 4• For each may-to-many relationship between entity sets E1 and E2 create a

link record type L and make it the member record type in two set types, of which the set type owners are the record types corresponding to E1 and E2.


LREC

Product/LRec SetManufacturer/LRec Set

Ron Smith 450 Maple St.

Gamma, Inc 68 Main St..

Bean Mfg. 26 Harris Ave.

115 Widget

116 Clamp

120 Gadget

1

2

3

4


LREC

Data Definition Language

• What is the DDL?

• Use the DDL to define the database schema

• The following procedure should be used.

Procedure

• Create the conceptual data model

• Map the conceptual data model to network data structure diagrams

• Use the DDL to implement the schema

A schema is made up of:

• Schema section

• Record sections

• Set sections

1. Create the conceptual model

CUSTOMER

LINE-ITEM

INVOICEHAS-

INVOICE1 M

1

CONTAINS

M

2. Map to a network structure

CUSTOMER

LINE-ITEM

INVOICE

CUSTINV

INVITEM

3. Implement the schema1. 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

17. OWNER IS CUSTOMER

18. MEMBER IS INVOICE

19. INVITEM

20. OWNER IS INVOICE

21. MEMBER IS LINE-ITEM

From Schema to Subschema

• Title division

• Mapping division

• Structure division• Subschema record section

• Subschema set section

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

Data Manipulation Language

• What is the DML?

• Process records one at a time

• The following procedure should be used.

Basic Commands

• Navigational commands

• Retrieval commands

• Update commands• Records

• Sets

Basic DML Commands

FIND

GET

ERASE

STORE

MODIFY

CONNECT

DISCONNECT

RECONNECT

Command

Navigation

Retrieval

Record Update

Set Update

Type

Some terms defined

• User working area

• Currency indicators

• Status flags

• Record templates

14 Bean 150

OWEDBY TEMPLATE

205 012505-31-99

INVOICE TEMPLATE

OWEDBY

INVOICE

OWEDBY-INVOICE

RUN-UNIT

CURRENCY POINTERS

10 Smith 100

14 Bean 150

16 Black 75

205 012505-31-99

210 024206-20-90

213 015506-29-99

User Working Area in Primary Memory

OWEDBY

INSTANCES

INVOICE

INSTANCES

Relationship of User Working Area to Database Instances

Retrieval and Update

• FIND Command

• GET Command

MOVE 105 TO CUST-ID IN CUSTOMER

FIND ANY CUSTOMER USING CUST-ID

GET CUSTOMER

A Simple Record Retrieval

MOVE 0 TO ACCOUNT-BALANCE IN CUSTOMER

FIND ANY CUSTOMER USING ACCOUNT-BALANCE

DOWHILE DB-STATUS = 0

GET CUSTOMER

(process customer record)

FIND DUPLICATE CUSTOMER USING ACCOUNT-BALANCE

END-DO

Retrieval of all Records with a Particular Characteristic

• ERASE Command

MOVE 0 TO ACCOUNT-BALANCE IN CUSTOMER

FIND FOR UPDATE ANY CUSTOMER USING ACCOUNT-BALANCE

DOWHILE DB-STATUS = 0

ERASE CUSTOMER

FIND FOE UPDATE DUPLICATE CUSTOMER USING ACCOUNT-BALANCE

END-DO

Deleting Records

• MODIFY Command


FIND FOR UPDATE ANY CUSTOMER USING CUST-ID

GET CUSTOMER

IF DB-STATUS = 0

THEN MOVE “455 Cherry Lane, Hamilton, Ontario” TO

ADDRESS IN CUSTOMER

MODIFY CUSTOMER

ELSE (perform error routine)

END-IF

Modifying Record Contents

• STORE Command


MOVE “James W. Smith” TO NAME IN CUSTOMER

MOVE “201 Scenic Drive, Hamilton,Ontario” TO ADDRESS IN CUSTOMER

MOVE 500.00 TO ACCOUNT-BALANCE IN CUSTOMER

STORE CUSTOMER

Adding New Records

Set Operations

• CONNECT Command

MOVE 231 TO INVNO IN INVOICE

MOVE “7/7/99” TO DATE IN INVOICE

MOVE 100.00 TO INVOICE-AMOUNT IN INVOICE

STORE INVOICE



CONNECT INVOICE TO CUSTOMER

Placing a Record in a Set

• DISCONNECT Command

MOVE 254 TO INVNO OF INVOICE

FIND ANY INVOICE USING INVNO

DISCONNECT INVOICE FROM CUSTINV

Removing a Record from a Set

• RECONNECT Command

MOVE 510 TO INVNO OF INVOICE

FIND ANY INVOICE USING INVNO



RECONNECT INVOICE IN CUSTINV

Changing Set Membership

Set Membership Classification

• Set insertion class

• Defined by the statement:

• INSERTION IS <insert mode>

• Manual insertion or Automatic insertion

• Manual Insertion Mode

• Must be placed by using CONNECT– CONNECT <record type> TO <set type>

SET NAME IS CUSTINV.

OWNER IS CUSTOMER

MEMBER IS INVOICE

INSERTION IS MANUAL

RETENTION IS OPTIONAL

Subschema Fragment




STORE INVOICE



CONNECT INVOICE TO CUSTOMER


• Automatic Insertion Mode

• Must be placed by using STORE– STORE <record type>






STORE INVOICE


• Set Retention

• Retention options are:

– Fixed

– Mandatory

– Optional

CUSTINV.

OWNER IS CUSTOMER

MEMBER IS INVOICE

INSERTION IS MANUAL


INVITEM

OWNER IS INVOICE

MEMBER IS LINE-ITEM

INSERTION IS MANUAL


Subschema Fragment

Implementation

• Large size

• Well-defined repetitive queries

• Well-defined transactions

• Well-defined applications

THE NETWORK DATA MODEL SECTION 8 An early DBMS. Background Networks are a natural way of representing relationships among objects The network data model.

Documents

record type r

set type owners

member record types

linking record

r slide

idms slide

simple network slide

n set types