Fichas
Databases
Fichas del conjunto (21)
- 1What is a database?It is an organised collection of related data. It is possible to add, edit, manage and retrieve data from a database. The structure of a database allows data to be found and used quickly.
- 2What is a record?It consists of a collection of related fields.
- 3What is a field?is a single item of data within a record.
- 4What is a table?It is a collection of related fields.
- 5Give examples of data types.Number (integer)
Number (real)
Text or string
Data/Time
Currency
Boolean
Lists
Picture
Sound
Video - 6What is a key field?A Key fields uniquely identities each record. No two records have the same data in their key field. Also known as Primary Key.
- 7What is validation?Data entered in to a database must be sensible or we get GIGO.
Validation methods can only ensure reasonable and sensible data is input in to a system, but there is no certainty that the data is correct.
Validation rules are needed for some fields. As data is entered it is checked to see that it obeys the rules; any data that does not obey the rules is not accepted. You can also set validation text – the text that appears if the data is not acceptable. - 8Give example of validation methods.Range check
Type check
Format/Picture check
Length check
Presence check
Lookup list - 9What is a report?A report is a printed document that contains data from the database, organised and analysed in a certain way. A report from a student database might list the students in each class in alphabetical order.
- 10Why are forms used?Forms are used to make data entry more attractive and secure rather than entering data into raw tables.
- 11What are calculated fields?Not all data needed in a report may be present in a database. For example a person’s age is never included because it changes day by day. If you want to use age in a report it must be calculated. This result is known as a calculated field.
- 12What are the uses of a database?Add, change or delete records
Search for a particular record
Sort the records into a given order
Print reports about some aspect of the database - 13Updating records.Records do not stay the same forever. They will need to be updated at some point. For example, people get married and change their surname, people move and change their address or prices of goods change.
Add a new record when a new pupil arrives to a new school
Edit existing records when someone move house
Delete an old record when an employee leaves a job - 14Searching for data.One main use a database is to find information quickly. To search for information you use a query. You are “querying the database”.
A query specifies what records you are searching for and what fields from the records you would like to display.
Simple query search (keyword search) – looks for data in one field.
Complex query search – looks at data with multiple criteria. - 15Operators= Equals
< Less than
> Greater than
<> Not equal to
AND Data is only listed where both conditions are true
OR Data is only listed where either or both conditions are true
LIKE Where a perfect match is not needed - 16What is a wildcard?You use wildcard searches in a query for data that you only know part of. For example find all the surnames beginning with ‘S’ you might write:
surname LIKE “*S” - 17Wildcards* Any number of characters
? Any character
[ ] Any character in the brackets
[ - ] Any character within a range of characters
! Any character not in the brackets - 18Sorting data.Results of queries can be presented in a sorted order e.g. alphabetical or in numerical order. Sorts can also be in ascending (A-Z) or descending (Z-A) order.
Why sort data?
• Easier if lists a printed as reports.
• You can identify best customer by amount they have spent – sort them according to total amount spent. - 19Security.If data is secure then:
• It cannot be destroyed
• It cannot be accidentally or maliciously altered
• It cannot fall in to the hands of unauthorized people
Consequences for a business where data is not secure include:
• Loss of customers – unhappy customers go elsewhere
• Payments for gods not being received
• Bad publicity – all businesses rely on a good reputation
• Management unable to make decisions due to lack of information
A number of methods are used to keep data secure:
• Physical security:
o Locks on doors
o Alarms
o ID cards
o Biometric systems - 20Software methods for keeping data secure.Passwords
Backups
Access rights can be placed on individual files - 21Benefits of using a database.• Fast access: using a database to find data is much faster compared to paper in a filing cabinet.
• Easy to edit: a database allows for data to be easily updated and changed.
• Validation: you can set checks on the data being entered to ensure no inappropriate data gets into the system.
Reports: results of searches can be used to print reports that may help management in their decision making. Sharing: database can be shared with any number of users on a network. Any user can edit the data.
Security: passwords may be set so that no unauthorized user can access the database, which may contain personal and sensitive data.