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21 Cards in this Set
- Front
- Back
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What are the characteristics of a relational database
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- Multiple tables
- Interconnected by relationships - With each one having a column and a row |
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Advantages of relational databases
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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 |
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What is a foreign key
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Is a field in a database which links to the primary key or part of it in another table
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What is a primary key
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A field in a database which uniquely defines the record
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What is a dbms system
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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
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Key features of a DBMS
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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 |
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Advantages of a DBMS
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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 |
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When is data in first normal form
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When there is no repeating attributes or group of attruibutes
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When is data in 2NF?
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when the data contains no partial key dependencies
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When is the data in 3NF?
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When the data relations contain no partial or transitive dependencies
The key, the whole key and nothing but the key ;)) |
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What are the advantages of normalization?
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- Reduces data redundancy
- helps to maintain data integrity - reduces storage and processing needs - otherwise data may become corrupted |
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What is a data warehouse/ warehousing
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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
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What is data mining?
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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
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What is a distrubited database
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stored data in more than one location over a lan/wan each location is a site
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What are the four types of distributed database
EXPLAIN WHAT THEY ARE |
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 |
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advantages of partitioned systems
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- less storage centrally
- local queries are quick -each site can customize database |
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disadvantages of partitioned systems
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-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 |
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advnatges of central systems
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storage needed once only
local indexes need minimal storage queries quick (all() always up to date high integrity |
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disadvantages of central systems
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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 |
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advantges of replicated systems
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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 |
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disavantges of replicated systems
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but
lots of storage needed data not up to date not for real time systems |
