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21 Cards in this Set

  • Front
  • Back
What are the characteristics of a relational database
- Multiple tables
- Interconnected by relationships
- With each one having a column and a row
Advantages of relational databases
1. Reproductivity - Less errors occour as the duplication of data is avoidable
2. Ssystem is future proof so it can hold a lot of data
3. secure - easy to control security as different user access levels can be established
4. Fluidity - it is dynamic, data does not need to be changed in all tables
5. allows reports and queries to be used

What is a foreign key
Is a field in a database which links to the primary key or part of it in another table
What is a primary key
A field in a database which uniquely defines the record
What is a dbms system
Software which allows management of data. it allows the data to be held in a structured form. allows discrete sets of data to be stored and rleationship interrogation
Key features of a DBMS
Allows database to be defined
allows querying of database
allows modification of data
allows modification of data structures
allows data to be exported and imported
Advantages of a DBMS
1. Data independence - where data is kept seperate from applications which use it. so a change in one will not effect functionality
2. Data consistency - any data written from application must adhere to validation rules. data should be same at processing input and output
3. avoids data redundancy - data held and stored once
4. data integrity high - no old data updated in all applications
When is data in first normal form
When there is no repeating attributes or group of attruibutes
When is data in 2NF?
when the data contains no partial key dependencies
When is the data in 3NF?
When the data relations contain no partial or transitive dependencies
The key, the whole key and nothing but the key ;))
What are the advantages of normalization?
- Reduces data redundancy
- helps to maintain data integrity
- reduces storage and processing needs
- otherwise data may become corrupted
What is a data warehouse/ warehousing
a dataware house is a large database used to store an organizations historical database for data mining purposes. Warehousing is where large quantites of data are collected from a range of sourses for data mining
What is data mining?
data mining is where data from a data warehouse is analysed to provide new information or to find new trends and patterns in existing data
What is a distrubited database
stored data in more than one location over a lan/wan each location is a site
What are the four types of distributed database
1. Vertically partitioned - different records are stored at different sites
2. Horizontally partitioned - different records stored at different sites based on fields
3. Central w/ remote indexes - data is stored in central locationeach site has locally stored index and commincate with central site to ask request to send whole data of record.
4. Replicated - each site has a copy of the whole database
advantages of partitioned systems
- less storage centrally
- local queries are quick
-each site can customize database
disadvantages of partitioned systems
-global queries take longer as comm link - needed
-global data deoendent on comm link
-customization must be controlled or data becomes unavailable
- no central backup
advnatges of central systems
storage needed once only
local indexes need minimal storage
queries quick (all()
always up to date
high integrity

disadvantages of central systems

powerful processing needed
if data isnt in index queries will be slower
all data dep on comm link
- no control over config
- needs fail safe system
advantges of replicated systems
all queries are quick
appropraite where updates not critical
extra fields can be added
natural back up - if one site loses its data can get another copy off another site
disavantges of replicated systems
lots of storage needed
data not up to date
not for real time systems