Question 5
What is a star schema?
A data modelling technique that maps multidimensional decision support data into a relational database
What does distribution transparency do?
Allows management of physically dispersed database as if centralized
What is the PK of a fact table?
Always composite because it refers to the many dimension tables. Always combines FKs from dimension tables.
What are the disadvantages of DDBMS?
Complexity of management control, technologically difficult, security, lack of standards @ db level, increased storage and infrastructure requirements, increased training costs, requires duplicated infrastructure
What does a star schema do?
Creates near equivalent of multidimensional database schema from relational data
What are the advantages of DDBMS?
Data are located near greatest demand site, faster data access and processing, growth facilitation, improved communications, reduced operating costs, user-friendly interface, less danger of single-point failure, processor independence
What are the DDBMS transparency features?
Distribution, transaction, failure, performance, hetergeneity
What are fact and dimension tables related by? What are they subject to?
FK, PK + FK constraints
What are the components of star schemas?
Facts, dimensions and attributes
What does a DDBMS do (Distributed DBMS)
Governs storage and processing of logically related data over interconnected computer systems. Both data and processing functions are distributed among several sites.
What is good about a star schema?
Its easily implemented and it preserves relational structures
What does location transparency require?
Just the name of the data fragments
What are the 3 levels of distribution transparency?
Local mapping, location, fragmentation
What is the relationship between the fact table and each dimension table?
M:1
What does fragmentation transparency require?
Neither, doesn't even need to know that the data is fragmented
What are facts?
Numeric values that represent a specific business aspect
What are facts and dimensions represented by in a star schema?
Physical tables in a data warehouse database
What are dimensions?
Qualifying characteristics that provide additional perspectives to a given fact
What does local mapping transparency require?
That the user specifies both the name and location of data fragments stored remotely
What is slice and dice?
The ability to focus on slices of the data cube for more detailed analysis
What are attributes used for in star schemas?
Used to search, filter and classify facts.