Jess.Bee.Happy! NA-NA-NA-NA-NA

Notes.

Wednesday, February 3, 2010

2:53 PM

Entity - A specific thing about which an information system collects and processes data. In a database of students, each student is an entity. Example entities for a school database system could include students, teachers, classrooms, etc.

Attribute - A field copied from a parent database. Attributes are the columns in a relationship table shown in list view. Attributes of a STUDENT may be name, date of birth, address, phone number, year advisor etc.

Normalise - The process of linking attributes within a relational database directly from original datafields, eliminating situations where attributes are linked to other attributes.

Calculated field - A field created by a calculation using data taken from other fields.

Hypermedia - Hypermedia is any display object that will link you to new information. Metadata is data that describes other data. Meta Data is used to control almost every aspect of the display on your screen so therefore in hypermedia it would control text colours, fonts and justifications, the positioning of texts and graphics, the links (both internal and external) and much more are controlled by placing HTML tags (metadata) in the file that builds the webpage. [eg websites and html codes used]

Data independence - means that the DBMS and its database are quite separate from each other.

Transaction file - the changes that occur in a particular time and eventually gets updated to the master file. Where there is a large number of changes to a databse - They create a temporary transaction file so that the master file which is the original database remains unaltered.

Record locking - Record locking is the technique of preventing simultaneous access to data in a database, to prevent inconsistent results. You don't have two people making edits and not knowing what will be saved at the same time.

Record - a data in a database.

Difference between shared and distributed databases ?
A shared database is stored on one computer but is available to all other computers on a network. There is a single online copy of the database, which makes data management and security much easier. A distributed database is split between several computers in the network. While no single computer stores the entire database, every record in the database is available to all users on the network.

Online storage - available for use and is fast. It is preferrable for databases that will be in constant use.

Offline storage - when a storage has to be loaded or inserted into a system before it can be used.

Incremental backups - only the files that have changed since the last full or partial backups would be copied.

Differential backup - all the files that have changed since the last full backup are copied.

[For larger databases its recommended to do one full backup and then incremental backups through out the week cause the full ones take too long]