In the name of Allah, Most Gracious, Most Merciful
Dr. Talal Maghrabi
THE WOLVES Group
Mr Omar Al-Shammari
Mr Sufyan Al-Malazi
Mr Rashed Labkhan
Friday, March 07, 2008

The Outline
I INTRODUCTION
II NETWORK MODEL
A Concept
B Logical Implementation
C Advantages and Disadvantages
III NETWORK DATABASE EXAMPLE
A Integrated Database Management System "IDMS"
CONCLUSION
REFERENCES

The network model was developed into a standard specification published by the CODASYL "Conference on Data
Systems Languages" Consortium in 1969 and its original inventor was Charles Bachman . It is a database model conceived as a flexible way of representing objects and their relationships, the network model allows each record to have multiple parent and child records, forming a lattice structure .
A. Concept:
In network database, data are represented by collections of records , and relationships between data are represented by links . A record in network database meets an entity in relational database. Thus, a record has a field or fields which meet attributes in relational database. But, a field can hold only one data value. A link is considered as a binary relationship in relational model.
Furthermore, a link is associates precisely two different records .
[Database Systems Concepts: Appendix A]
B. Logical Implementation:
Logical structure of network database is described by data-structure diagram . In such a diagram there are two main components: First is boxes which represent records. And, second is lines which represent links. [Database Systems
Concepts: Appendix A]
Links are of three types: Many to many, one to many, and one to one links. [Database Systems Concepts: Appendix A]

Figure 1: A simple ER Diagram.
Figures 1-8 are courtesy of Database Systems Concepts 5 th Ed . printing rights holder.
Figure 2: Corresponding Network model diagram for ER diagram in Fig. 1.
Figure 3: A sample of 1:N link in which a customer may have multiple accounts but not vice versa.
Figure 4: A sample 1:1 link in which a customer can only have one account and vice versa.
Tertiary relationships can be represented in network model by: Creating a new record. Then, each value is represented by a field. Next, the new record is connected with other records with appropriate types. So, the new record links between two records and stores some required values that cannot be held in either of them. [Database Systems Concepts:
Appendix A]

Figure 5: An ER diagram that has a tertiary relationship.
Figure 6: Corresponding network model of figure 5.
DBTG Model:
It is a database standard specification that has been developed in the late 60s by Database Task Group (DBTG), and called the CODASYL DBTG 1971 report. [Database Systems
Concepts: Appendix A]
In DBTG Model, many to many links are disallowed.
Thus, same trick used with tertiary relationships is used with
DBTG Model. For many to many links, a new empty of fields record is created. Then, two one-to-many links are created between corresponding records with the empty of fields record in the middle. Also, DBTG sets have been introduced. DBTG sets are consisted of a parent (owner) record and may contain zero child (member) record or more. Furthermore, DBTG Model allows for multi-valued fields by what they call: Group repetition. In group repetition, some fields of a record are to be repeated to fit different values. For example, a customer of two addresses has fields of address of customer record repeated as necessary to fit his addresses. [Database Systems Concepts:
Appendix A]

Figure 7: A DBTG Set Example; where A is the parent record, and B is the child record.
Figure 8: DBTG group repetition example.
Queries go through navigational style of data access that is called "walking the set". Links are named to allow going through any link to get to records. Thus, a record has several ways to be caught. [Databases Demystified – Chapter 1: 12-13]
Figure 9: A complicated sample of network model of a company; where bold, dashed and dotted arrows indicate links.
Figure is courtesy of Databases Demystified by Andrew Oppel printing rights holder.

C. Advantages and Disadvantages:
Advantages:
In that time when there was only hierarchical model, the network model had greater flexibility for handling complex spatial relationships. Also, for performance issues, at the time relational model was invented, network model used to persuade for large-scale applications. [Databases Demystified – Chapter 1:
12-13]
Disadvantages:
Complexity of design and implementation is a major drawback of network model. Since, a staff has to be very familiar a database to work through its set structures. Also, navigational style, which in some cases might be considered as an advantage than hierarchical model, may lead to a dead end.
[Databases Demystified – Chapter 1: 12-13]
A. Integrated Database Management System " IDMS":
The roots of IDMS go back to Dr. Charles Bachman's IDS
(Integrated Data Store), an early database engine developed at
General Electric .
The main structuring concepts in this model are records and sets .
Records essentially follow the COBOL pattern, consisting of fields of different types: this allows complex internal structure such as repeating items and repeating groups ..
Sets are generally maintained as linked lists, using the database key as a pointer .
Every record includes a forwards link to the next record; the database designer can choose whether to include owner

pointers and prior pointers (if not provided, navigation in those directions will be slower .)
IDMS organizes its databases as a series of files. These files are mapped and pre-formatted into so-called areas. The areas are subdivided into pages which correspond to physical blocks on the disk. The database records are stored within these blocks .
Some versions of IDMS subsequently included the ability to define indexes: either record indexes, allowing records to be located from knowledge of a secondary key, or set indexes, allowing the members of a set to be retrieved by key value .
Figure 10: IDMS Interface
Figure is courtesy of UMBC.

CONCLUSION
Although the model was widely implemented and used, it failed to become dominant for two main reasons. Firstly, IBM chose to stick to the hierarchical model with semi-network extensions in their established products such as IMS and DL/I.
Secondly, it was eventually displaced by the relational model, which offered a higher-level, more declarative interface.

1. THE HANDBOOK OF COMPUTER NETWORK
Volume 3 , Hossein Bidgoli
2. NETWORK MODELS AND ASSOCIATED APPLICATIONS
Baker
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INTERNATIONAL JOURNAL OF NETWORK
MANAGEMENT
John Wiley
4. DATABASES DEMYSTIFIED
Andrew Opple, E-Book.
5. DATABASE SYSTEM CONCEPTS
Abraham Silberschatz, Henry F. Korth, and S. Sudarshan 5 th
Edition