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.