Dear fahd,
Thank you for your question.
Nick Rossiter says:
"...The network model is based on directed graph theory and the
relational on functions and relations. The hierarchical is a special
case of the network model with a restriction on the linking mechanism.
"
http://216.239.35.100/search?q=cache:L1i-6GoPkHAC:www.cs.ncl.ac.uk/people/b.n.rossiter/home.informal/envirs96.ps+compare+contrast+relational+hierarchical+network&hl=en&ie=UTF-8
Case contains more detailed definitions.
The presentations by Robert Zmud from Oklahoma University , C. Karazai
and Case provide a good basis for your answer and also covers some
areas of your other Google questions. I think the relative advantages
and disadvantages almost “fall out” from an understanding of the
structures of the various models (please refer to presentation
graphics) , combined with the goals of database design as outlined by
Karazai:
- data independence
- data integrity
- data redundancy
- data security
All models would have the advantages of a database compared to flat
files:
“- reduced redundancy
- increased data integrity
- increased flexibility
- increased ability to share data
- increased security” (Zmud)
Hierarchical Advantages
- conceptually simple
- efficient for 1 to many relationships fixed over time.
Hierarchical Disadvantages
- management difficulties caused by parent segment deletion in that
all child segments must also be deleted
- Lacks structural independence ie Must know the path and changes
require a change of path
- A child cannot have multiple parents (Case)
Network Model Advantages
- data independence ie changes in data do not necessitate program
changes
- handles more relationships than hierarchical eg a child can have
multiple parents
Network Disadvantages
- detailed structural knowledge is required
- lack of structural independence
However, the relational database has advantages when compared to both
the network and hierarchical structures:
- good for ad hoc requests
- simpler to navigate (see hierarchical diagram in Case)
- easier to maintain than network and hierarchical
- easier to add data
- greater flexibility
- greater data independence
Relational disadvantages:
- significant hardware and software overhead
- may have slower processing times than hierarchical and network
- not as good for transaction process modelling as hierarchical and
network
Zmud, Robert, Database Management Overview
http://www.ou.edu/zmud/BAD5153/Lecture-8.ppt
Karazai, C., Lecture3: Database Models
http://www.staff.brad.ac.uk/ckarazai/Lecture3.pdf
Cales, File Systems and Databases
http://faculty.mgmt.okstate.edu/~cales/chap1-2.ppt
Search strategy
compare contrast relational hierarchical network
advantages OR pros relational hierarchical network
Regards, |
,
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