Week 10 Flashcards
What is a Distributed Database?
Collection of multiple interconnected databases, which are:
- Spread physically across various locations
- Communicate via a computer network
What are the 2 desired characteristics of Distributed Databases?
- Distribution/location transparency:
- Users perceive the database as a single, logical entity
- Local Autonomy
- Local data is locally owned and managed
- Each local database operated independently
- Local systems are able to operate effectively even if remote databases are not available
What are the 2 types of Distributed Databases?
Homogeneous
Heterogeneous
What is a Homogeneous Distributed Database?
All sites use the same type of DBMS
What is a Heterogeneous Distributed Database?
Sites run different DBMs
Translate using gateways: convert the language and model of each different DBMS into the language and model of the relational system
What is Fragmentation?
Fragmentation is to divide a table into a set of smaller tables to be stored in different sites. The subsets of the table are called fragments
Types of fragments:
-Horizontal
Subsets of rows are stored at different sites
-Vertical
Subsets of attributes are stored at different sites
-Hybrid (mixed)
What is Data Allocation?
The process of assigning each fragment to a particular site in the distributed system
What are the 2 types of Data Allocation to allocate fragments?
Fully replication
A complete copy of the DB at each site
Non-redundant allocation
Each fragment stored at exactly one site
What are the advantages of a Distributed Database?
Reflects organizational structure
Easier expansion
Increased reliability and availability
Better response/improved performance
What are the disadvantages of a Distributed Database?
Complex to design and implement
Harder to control security and integrity
Lack of standardisation
What is a Data Warehouse?
Is a database, which:
-Is kept separate from the organization’s operational database
-Possesses consolidated historical data
-Helps the organization to analyse its business
What are the key features of a Data Warehouse?
Subject Oriented - eg., a sales data warehouse, or a credit card transaction data warehouse, etc.
Integrated - Data combined from multiple sources
Time Variant - Looking for changes over time
Non-volatile - Previous data is not erased when new data is added to it. Frequent changed in operational database is not reflected in the data warehouse
What is Online Analytical Processing (OLAP)?
Uses multi-dimensional view of aggregate data to provide quick access to strategic information
What is Data Mining?
Process of discovering meaningful new correlation, patterns and trends using statistical, mathematical, and artifical intelligence (AI) techniques
