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14 Cards in this Set
- Front
- Back
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Data Files consist of
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Field - characteristics of the column
records - group of related fields |
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Problems with storing data in files
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Presence of redundant data
Inconsistent data |
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Define entity and relationships
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Entity - object about which you want to store data
Relationships - Links that shows how diff. records are related |
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Primary Key
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Column in table whose value is unique for each row
every row must have a primary key Cannot be null |
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Candidate Key
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any column that could be used as the primary key
should be a column that is unique for each record and does not change |
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Surrogate Key
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column created to be records primary key identifier
Has no real relationship to row other than to identify it uniquely values automatically generated using a sequence |
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Foreign Key
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column in table that is primary key in other table
creates relationship between 2 tables Value must exist in table where it is the primary key |
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Composite Key
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Unique key that is created by combining two or more columns
Usually comprises fields that are primary keys in other tables |
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Database system
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2 parts:
-DBMS Manages physical storage and data retrieval -Database applications Provide interface that allows users to interact with database |
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Server/Client database
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-Server
Computer that shares resources with other computers -Client Program that requests and uses server resources |
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Server process
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Program that listens for requests for resources from clients Responds to requests
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Personal DBMS
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DBMS and database applications run on same workstation
Appear to user as a single integrated application Used primarily for creating single-user database applications Only used for non-mission critical purposes |
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Client/Server DBMS
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DBMS server process runs on one workstation
Database applications run on separate client workstations across network Server sends only requested data back to client rather than entire database |
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Advantages of a client/server DBMS
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Generate less network traffic than personal databases
Extra features to minimize chance of failure Powerful recovery mechanisms that often operate automatically Maintain file-based transaction log on database server |
