Network Data Model

Software Engineering

1971 and 1978.

Network data model was proposed that supports

– elementary named data. Its instance (occurrence) is a data value.

TEACHER

Name

Post

Address

Record type instance – ordered collection of fields instances:

TEACHER

Johnson

professor

Kiev

may have duplicate values of all data items.
The Data Base

CALC key is an internal identifier of any record, that assigned to a record on the base of values of a specified record fields.

level hierarchical relationship of the record types. With the help

Set owner. There is only one set owner record
Set members. There may be 0, 1 or more set member records.

Set instance (occurrence) consists of one instance of the owner record type and any number of instances of the member record types

Thus the set represent two level hierarchical one-to-many relationship.

TEACHER

SUBJECT


logics
DBMS

С language


Peter
John

Ann

SE
Department Structure
Set owner
Set

Set type Set instance

Set name

Structure

BOOK

ARTICLE
Scientific Works
Owner

Members of the set «Department Structure»

Owner of the set «Scientific Works»

Members of the set «Scientific Works»

Department Structure

BOOK

ARTICLE
Scientific

GROUP

LECTURE

Attend

Is taught at

Has

m:n

m:n

SUBJECT

LECTURE
Is_taught_at
Has
Teachers
Lectures
Subjects

SUBJECT

Is_taught_at

Has

TEACHER

PART
Consists of
Consists of
Cycle

locates a described record occurrence
GET - reads a record occurrence

located. Located record occurrence becomes current. Current status indicator in

FIND

Puts selected (current) record into UWA.

GET

[variable]
Syntax:
Example:

X=10;
FIND Faculty RECORD BY DATABASE KEY X;
If Error_Status=0

record directly using known values of its fields, such fields

FIND [record-name] RECORD BY CALC-KEY

Syntax:

Example: Find lecture record with LID field value “L3” (Field LID is defined as как CALC-field)

Lecture.LID = "L3";
FIND Lecture RECORD BY CALC-KEY;

as a “ring” consisting of the owner record and all

SUBJECT

LECTURE

Is_taught_at

Has

TEACHER

RECORD IN [set-name] SET
Syntax:
Example:

FIND NEXT Lecture RECORD IN Has SET;

RECORD IN [set-name] SET
Syntax:
Пример:

FIND PRIOR Lecture RECORD IN Has SET;

occurrence


FIND FIRST|LAST [record-name] RECORD IN [set-name] SET
Syntax:
Example:

FIND FIRST Lecture RECORD

Current occurrence of the set “Has”

L1 - the first member record of the set “Has”

Error_Status != 0 – the record occurrence do not have member records

L1 L2 L3 L4 L5

S1 S2 S3

T1 T2

OWNER OF [set-name] SET
Syntax:
Example:

FIND OWNER OF Has SET

LAST Lecture RECORD IN Has SET;
FIND OWNER OF Is_taught_at SET;
FIND

T1
L3
S2
L4
L5
S3

in UWA;
execute the command STORE.

STORE [record-name] RECORD
Syntax:
Example:

STORE Teacher RECORD
Stored record

set occurrence the current of set type
Make inserted record occurrence

INSERT [record-name] RECORD INTO [set-name] SET

Syntax:

Example:

X = 31; FIND Teacher RECORD BY DATABASE KEY x;
Y = 24; FIND Lecture RECORD BY DATABASE KEY y;
INSERT Lecture RECORD INTO Has SET;

certain set occurrence
Make designated record be the current one
Execute the

REMOVE [record-name] RECORD FROM [set-name] SET

Syntax:

Example: Remove all lectures of the teacher with DBK 31.

x=31; FIND Teacher RECORD BY DATABASE KEY x;
Loop: FIND NEXT Lecture RECORD IN Has SET;
IF Error_Status=0 THEN BEGIN; REMOVE Lecture RECORD FROM Teacher SET;
GO TO Loop;
END;

in UWA into the current record occurrence of the DB.

Example: For teacher with DBK 31 change name to “Smith”.

x=31; FIND Teacher RECORD BY DATABASE KEY x;
GET Teacher RECORD;
Teacher.Name = ”Smith”;
MODIFY RECORD;

the current record occurrence
The set owner may be deleted

DELETE [record-name] RECORD

Syntax:

Example: Delete record with DBK 21.

x=21; FIND Lecture RECORD BY DATABASE KEY x;
DELETE Lecture RECORD;

advantages and drawbacks as hierarchical data model.

The only basic difference