Databases Reference
In-Depth Information
Exhibit 18-20.
Chart of pitfalls and remedies.
Modeling
Areas
Possible Pitfalls
Plausible Causes
Entities
1.
Missed entities
• Did not explore all possible avenues to
capture them
• Paid too close attention to existing
systems rather than new requirements
2.
Imposter entities
• Confused with paper documents
• Created just to appease users
3.
Modeled abstract
concepts using
concrete entities
• Wrong level of abstraction
• Did not recognize that data modeling
requires more precision than common
use of English terms
Relationships
1.
Unidentified
relationships
• Did not explore all possible avenues to
capture them
• Paid too close attention to existing
business rather than new requirements
2.
Misconstrued
relationships (when the
entity name coincides
with document name)
• Did not differentiate document from
entity in case of coincidence in entity
and document name
3.
Redundant
relationships
• Cannot tell whether a relationship is
redundant
• Indirect relationship was discovered
before the direct relationship
4.
Spurious relationship
• Indirect or spurious relationship was
discovered first and overshadowed the
real relationship
5.
Access path serves
relationship
• Physical design considerations
overrides logical
6.
Inconsistent semantics
in relationships
• Lack of user input as to which one of the
two semantics is germane
• Potentially, a new relationship could be
useful
Entity
Subtypes
1.
Multilevel subtype
going too deep
• Possible improper choice of subtyping
criteria
• Did not carefully assess the real need
for further subtyping
2.
Multiple supertypes for
one subtype
• Confused with role situation
3.
Omission of needed
supertype
• Overlooked attributes that need to be
stored in supertype
Role Entities
Failure to identify needed
role entities
• Confused with supertype-suptype
situations
• Did not know of role concept
Time-Related
Situations
Incorrect cardinality on
time-related entities
• Model did not reflect the time
dimension requirement-assuming
snapshot when it is perpetual or vice
versa
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