Database Reference
In-Depth Information
Confirmation of logical design. Describe the procedure used for having the
logical data model reviewed with user groups. State the results of the reviews
and any special requests for revisions.
CHAPTER SUMMARY
The logical data structure represents how data are perceived; in a relational
data model, logically, data are perceived as two-dimensional tables.
The physical data structure refers to how data are stored in physical storage.
The logical data design phase in DDLC defines the logical structure of data.
This phase is a prerequisite for physical design.
Users understand the logical structure of data better than physical structures.
The logical design phase is necessary to produce the logical structure that can
be used to communicate with users.
The design effort is easier and more manageable when it is divided into logical
design and physical design.
The outputs of the logical design phase are used as inputs in the physical design
phase.
The first part of the logical design phase consists of creating a semantic data
model truly representing real-world information requirements.
In the second part of the logical design phase, the generic semantic data model
is transformed into the desired logical data model. To implement a relational
database system, the semantic data model is transformed into a relational data
model.
Entities, attributes, relationships, and rules and constraints are represented in
the target relational data model.
CASE tools offer major benefits during the logical design phase.
The issuance of the logical design documentation marks the conclusion of the
logical design phase and the commencement of the physical design phase.
REVIEW QUESTIONS
1. Distinguish between logical data structures and physical data structures.
2. Explain briefly the difference between logical and physical data structures in
a relational database system.
3. Describe briefly how and where logical design fits in the database develop-
ment life cycle (DDLC).
4. List any three reasons why the logical design phase is necessary.
5. “The output of the logical design phase forms the input to the physical design
phase.” Explain briefly.
6. Completing the logical design phase involves ensuring design completeness.
List any four critical factors for consideration in the review for design
completeness.
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