INFO 340 Study Guide - Quiz Guide: Candidate Key, Unique Key, Check Constraint
Quiz 3 Notes
What, why, how + what will happen if not done correctly (impact)
Explain differences between composite, multi-valued and derived attributes and provide
examples of each.
- Context: identified in conceptual phase, further normalized during logical design phase,
developed/coded during physical design phase
- Valuable b/c if done incorrectly → worry about processing + performing at all phases of
development → will miss normalization if these attributes are not understood
- Why: when addressing performance + normalization, helps us understand user’s
perspectives
- If done poorly → have poorly designed database
o Have data in application competing with itself to be processed
▪ Increased locking + blocking
▪ Added performance overhead
o How?
▪ If compute information every time it’s referenced, such as GPA, will end
up with unnecessary processing
- Differences
o Composite attributes – attribute composed of multiple components
▪ Example: address attribute can be subdivided into street, city, + postcode
▪ Dependent on whether need to refer to as single unit
o Multivalued attributes – attribute with multiple values for each entity type
▪ Each entity instance can have more than one value
▪ Example: multiple phone numbers for one person
o Derived attributes – value derivable form value of related attribute or set of
attributes
▪ Implement if highly read but infrequently changed
▪ Why? To automate calculations + minimize human error
▪ Example: student GPA
Explain decisions designers make in regards to establishing each primary key; what is the
preferred data type and configuration settings? Why?
- Candidate key – any column or columns that can uniquely identify a row
o Important b/c helps us write efficient queries
▪ How – security, normalization, indexing/query optimization
Document Summary
What, why, how + what will happen if not done correctly (impact) Explain differences between composite, multi-valued and derived attributes and provide examples of each. Context: identified in conceptual phase, further normalized during logical design phase, developed/coded during physical design phase. Valuable b/c if done incorrectly worry about processing + performing at all phases of development will miss normalization if these attributes are not understood. Why: (cid:449)he(cid:374) addressi(cid:374)g perfor(cid:373)a(cid:374)(cid:272)e + (cid:374)or(cid:373)alizatio(cid:374), helps us u(cid:374)dersta(cid:374)d user"s perspectives. If done poorly have poorly designed database: have data in application competing with itself to be processed. To automate calculations + minimize human error: example: student gpa. Candidate key any column or columns that can uniquely identify a row. Important b/c helps us write efficient queries: how security, normalization, indexing/query optimization. Primary key uniquely identifies each occurrence of an entity type: critical to establishment of relational theory, choosing primary key when certain of future uniqueness + attribute length.
