question (1 Viewer)

[harvestcows]

ermm..can anyone list all the advantages of a normalised relational database versus a flat file database
i've got

-much more flexible in design
-reduction in redundant data
-takes up less space as redundant information is reduced
-greater overall database organisation


-easier to manage e.g. changes to a particular item e.g. student age only need be changed once
-greater data consistency and thus greater data integrity. e.g. once an age for student is changed then all respective ages for student are changed and there are no inconsistencies in age

 

[Pace_T]

quicker data access/retreival as the database is smaller in size (despite an increase in tables)

 

[Lwaxana]

Advantages
Data redundancy - avoids repetition
Data integrity - easier to organise, maintain and update
Data security - easier to achieve, levels of access
Data quantity - works efficiently with large amounts of data

 

[harvestcows]

hmm okay but can you expand on

Data security - easier to achieve, levels of access
Data quantity - works efficiently with large amounts of data

also i know what primary/composite/secondary/foreign keys are but what is a key field and is an index key the same thing as a primary key

 

[Lwaxana]

Data security protects data against unauthorised use. DBMS have inbuilt security facilitis and allow multiple levels of security. Obvioulsy this wouldnt work in a flat file. With a relational - imagine school one - students might be able to see other students names - but only staff could see their home address and phone number.
So data can be made available to users with different levels of authorisation - or may be set that everyone can view data but only some can modify/delete it.

As you said they can handle huge amounts of data and with little redundancy the overall file size should be minimised - economy of scale is much easier to attain.

All u need to know about keys is on pgs 44-6 of Heinemann
A key field is a field of a database table that holds unique data which identifies that record from all the other records in the file or database. Account number, product code and customer name are typical key fields. As an identifier, each key value must be unique in each record.

 

[SamD]

also i know what primary/composite/secondary/foreign keys are but what is a key field and is an index key the same thing as a primary key

Specifying an index on a field causes the DBMS to maintain a sort order on that field. The records are not physically sorted on the field, rather an index is created with the field so that sorting is greatly simplified.

For example, in a Client table, ClientID may be the primary key that links clients to other tables (all primary keys are indexed). However it would be common to sort and search on client's surnames hence the surname field would be a good choice for another index. You shouldn't add indexes to all fields because there is a performance overhead required to maintain the index when adding or editing records.

HTH
Sam