Flashcards
Topic 5 ICT
Flashcards do conjunto (25)
- 1What is an entity?An item about which you can store and share data. Eg CUSTOMER, SUPPLIER, ORDER
- 2What is a table?The physical realisation of an entity. It is made up of records and fields.
- 3What is an attribute?A characteristic of an entity – eg surname, telephone number
- 4Field?A field holds a single data item. It is the physical realisation of an attribute.
- 5Record?A row of a table that contains all the data about a person or object that the record describes.
- 6Primary key?A field which uniquely identifies a record in a table.
Primary key can be:
1 Simple – made up of single field like StudentID, ProductCode
2. Compound/composite – made up of more than one field like: EventName and EventDate - 7Foreign Key?A field in one table which is the primary key of another table. It is used to link tables in databases.
- 8Relationship?A link between two tables in a relational database.
- 9Referential IntegrityThis ensures that it is impossible for the user to enter a value in the foreign key a of table if the value does not exist in the primary key of the table to which it is linked. Eg the user cannot specify that a student in the STUDENT table has a tutor who isn’t in the TUTOR table.
- 10Duplicate Data?Data that is repeated within database tables.
BAD because
• Increases memory space required - 11Cascade Delete?• If a record is deleted from one table, then the related record in all other tables is deleted.
- 12Cascade update?• If a record is updated in one table, then the related record in all other tables is updated accordingly.
- 13What is a Relational database?Many tables, linked together via primary and foreign keys.
- 14Advantages of Relational databases• No data duplication.
• If necessary, you can cascade delete, or cascade update. - 15Disadvantages of Relational databases• Complexity – not good for novice users – need an expert
• Complex software required, which is more expensive. - 16Entity-Relationship diagrams: Give three examples?1:1 (one-to-one)
1:m (one-to-many)
m:m (many to many) - 17What is normalisation?A normalised database has minimal data duplication.
This is achieved by breaking down a single table into several smaller tables, removing repeating groups, ensuring each table has a unique primary key and that each field is atomic. - 18Three stages of normalising a database1NF – No repeating groups. All fields are atomic (Eg name should be broken down into firstname and surname)
2NF – Every field depends on the whole of the key.
3NF – Every field depends directly on the key and not indirectly on it. - 19Name some items in a data dictionary?• Names of each table
• Names of each field in each table
• Data Type of each field (Eg text, Integer etc) - 20Types of Query:select queryextracts data from one or more tables.
- 21Types of Query:parameter queryselects data from one or more tables according to criteria specified in the criteria row.
- 22Query: dynamic parametero Asks the user for some data
o Selects the records in the table which match the users data. - 23Static query?the parameter is entered directly into the query design grid: Product Category: “Women”, “Men”, etc
- 24What is the difference between a simple and complex query?Simple: One parameter
A complex query is one that contains more than one parameter, which can be joined together using AND, OR and NOT. - 25What are action queries used for?to change the data in the database.
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- FlashCards sobre Topic 5 ICT, criado por amy.collier em 28-05-2014.
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- amy.collier
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