Sorting Text&Numbers
Tuesday, February 9, 2010
2:46 PM
If you sort the list above in text format you would get
1, 100, 11, 2, 3 however if you sort the same numbers using a number format you would get 1, 2, 3, 11, 100 (if we were using ascending order of course)
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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]
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Monday, February 1, 2010
9:13 AM
Paper (Manuel) - Hard copy
Flat File - type of database where all of the data is contained in one file. For all of the information to be held in one table, every student record would require data to be unnecessarily duplicated, introducing redundant data
Relational Database - collection of data items organized as a set of formally-described tables from which data can be accessed or reassembled in many different ways without having to reorganize the database tables. Store alot of information.
Hypermedia - a multimedia system in which related items of information are connected and can be presented together. Can be access anywhere, depending on security levels. (not the best because of security).Passwords,
Personnel Records - documenting the management of employees are important records in all organisations.
Encription - encoding: the activity of converting data or information into code
Level of Access - how much can be accessed. Eg age groups, or position (boss vs emmployee)
Data Dictionary - Meta Data [data about data] , A data dictionary is a table providing a comprehensive description of each field in the database. This commonly includes: field name, data type, data format, field size, description and example.
Schema - the organisational structure of a database. It should show the entities (the tables in the database), and their characteristics (i.e. their properties/attributes/fields). It should clearly identify the primary key in each table and the links and relationships between tables. The example below is just one way a schema can be represented.
Defined as an organised plan of the entire database showing how and where the data is to be found, descriptions of the data, and their logical relationships.
Primary Key - primary key is a character or group of characters used to identify a unique record in a database. The key is composed of one or more fields from the record.
Data validation - as a check on entered data to ensure that it is of the correct data type and that its value is sensible. If anything other then 'M' or 'F' is entered into the 'Gender' field, the entry will not be allowed and a warning message will be displayed. This will assist accurate data entry.
Query language - the method of formulating queries in an information retrieval system to retrieve data. A query language builds search specifications using relational and logical operators. Relational and logical operators compare expressions that make up the search specification.
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