Chapter 16- relational databases

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what is a database?
A database is an organised, structured collection of related data, designed to allow aaccess by a number of different applications. It holds information about ENTITIES in a series of related TABLES
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what is a Flat File?
A flat file is a single TABLE often stored as a plain ASCII text file. When viewed on screen it looks similar to a spreadsheet. Compared to a RELATIONAL DATABASE, not very flexible, simple operations such as sorting and filering can be carried out
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what is data integrity?
it refers to the completeness and accuracy of data. Data duplication and redundancy can also compromise data integrity since several contradictary versions of data exist at once
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What is data consistancy?
a particular attribute has only one value at a particular time. a change to a data value is implemanted throughout the database because it is held onlly in one table
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what is data redundancy?
the same value is stored more than once thus taking up unnecessary space e.g airport names/flight dates/departure times/arrival times are stored in every record
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what is data independence?
seperation of data from processing, either so that changes in the size or format of the data elements require no change in the computer programs processing them or so that these changes can be made automatically by the database management system
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what is a primary key, a composite key and a forgin key?
primary- is a feild that uniquely identifies a feild or a row e.g customerID. Composite- 2 or more kay feilds eaach of which may be primary in another table and unique ID. Foregin- primary key in one table but attribute in another
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what is normailsation?
normalisation is the process of simplifying complex tables by dividing them into separate related tables. This leads to an efficient database design that avoids duplication and redundancy.
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What are the benefits of normalisation?
data redundancy is eliminated- minimises the storagge requirements. Data consistency is ensured- an attribute wil only have the onee value. improved data integrity. improved data independence
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The stages of normailisation
1NF- removes any repeating groups. 2NF- removes fields not dependant in the whole primary key, remove any non key depnedencies. 3NF- removes fields that depend on non key fields
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what is a DBMS?
It is the software used to manage the operation of databases. it performs a number of useful functions, including presenting data to the user and manageing security.
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what does that database deigner do?
decides how the data is stored and organised. ensures data will be held securely. providing means of accessing data that meet the needs of each type of user. creating access levels. fully documenting the design of the DB including Data Dictonaries
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what does the database administrator do ?
responsible for the day-to-day maintenance of databases. However it is normal for a DBA's job to occasionally include database design.
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what is a data dictonary?
it defines the type and the format of the data and the relationships between dtata. this is initially created at the analysis and design stages to provide a record of the data requirements.
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Card 2

Front

what is a Flat File?

Back

A flat file is a single TABLE often stored as a plain ASCII text file. When viewed on screen it looks similar to a spreadsheet. Compared to a RELATIONAL DATABASE, not very flexible, simple operations such as sorting and filering can be carried out

Card 3

Front

what is data integrity?

Back

Preview of the front of card 3

Card 4

Front

What is data consistancy?

Back

Preview of the front of card 4

Card 5

Front

what is data redundancy?

Back

Preview of the front of card 5
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