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Relational Databases
Higher Info Sys Relational Databases
| Term | Definition |
|---|---|
| data duplication | problem created by the same items of data being entered in more than one place - leads to data inconsistency |
| insertion anomaly | problem that arises when it is not possible to add a new record (data on one thing or person) without knowing information about something else |
| deletion anomaly | problem that arises when deleting a record (data about one thing) also deletes data about something else |
| modification anomaly | problem that arises when data needs to be amended in a record but due to data duplication appears in several records - failure to update all records lead to inconsistency |
| meaningful identifier | problem that arises by using a key field which has meaning - often needs to be altered when changes occur in circumstances but keys should never be changed |
| entity | thing about which data is stored - represented in a table. |
| single valued attribute | a field which holds only one occurrence of data |
| multi valued attribute | a field which holds more than one occurrence of data |
| data domain | the area or topic about which data is stored, e.g.. Video Rentals |
| domain constraints | conditions placed on the data or attributes to specify exactly what data can be stored |
| data type | the kind of data to be held in an attribute |
| integer data type | kind of data containing positive or negative whole numbers with no fractional part |
| real data type | kind of data containing positive or negative numbers which may have a fractional part |
| text data type | kind of data containing letters, digits or symbols |
| object data type | kind of data containing a picture, video clip or sound clip |
| link data type | kind of data containing a reference to another item of data such as a pathname to a file location or a URL to a web resource |
| Boolean data type | kind of data containing one of two values - TRUE or FALSE |
| date data type | kind of data containing day/month/year |
| time data type | kind of data containing hr:min:sec |
| cardinality | measurement of a relationship (one to one, one to many, many to many) |
| entity relationship | relationship between to entities |
| entity occurrence diagram | graphical representation used to demonstrate the relationship between data items in entities |
| entity relationship diagram | graphical representation of relationships between entities |
| primary key | unique attribute(s) used to identify an instance of an entity (a row in a table) |
| foreign key | an attribute in one entity that is the primary key in another entity |
| compound key | a key made up of more than one attribute |
| candidate key | an attribute (or set of attributes) which may be selected to uniquely identify each instance |
| surrogate key | a piece of data invented by the user to uniquely identify an instance (used to avoid meaningful identifiers) |
| non meaningful identifier | unique item of data with no meaning - good for primary key |
| data integrity | the accuracy of data during and after processing - can be enforced through data validation techniques |
| referential integrity | associated with foreign keys - this requires that every foreign key must have a related value entered in the primary table |
| entity integrity | associated with primary keys - this means that a new record cannot be entered without a value in the primary key attribute. This ensures non-NULL primary key and no multi valued attributes |
| validation | a series of checks carried out by the software to ensure data entered is accurate and sensible and meets certain criteria |
| validation: presence check | a check included in the system to ensure a value is entered into the attribute - it cannot be left empty |
| validation: range check | a check included in the system to ensure a value entered is between an upper and lower limit |
| validation: restricted choice | a check included in the system to ensure a value is selected from a preset list of possible values |
| data dictionary | a collection of data describing the data in the database (metadata about the database system) |
| data dictionary: attribute name | describes each single item of data - giving a unique title and explanation of the item |
| data dictionary: attribute type | describes the kind of data to be stored in an attribute |
| data dictionary: attribute size | describes the maximum number of characters allowed in the attribute |
| data dictionary: index | used to speed up searching and sorting of records by giving them an order number and storing this information separately. Should be used on key fields and other fields which are commonly used for sorting |
| data dictionary: validation | describes the checks to be carried out on each attribute |
| data entry using lookup | method used to put data into attributes without retyping it - it references the original location in another table - helps maintain data consistency |
| normalisation | a step by step process for analyzing data to establish entities required, establish which attributes belong to each entity, define relationships between entities and minimize the duplication of data |
| un normal form (UNF) | stage of normalisation to list all data items in the current data model |
| first normal form (1NF) | stage of normalisation to eliminate repeating groups |
| second normal form (2NF) | stage of normalisation to remove partial key dependencies |
| third normal form (3NF) | stage of normalisation to remove non key dependencies |
| data retrieval | getting data back from where it is stored |
| database form | a view of a database usually used to enter data one record at a time |
| answer table | a view of a database showing the results of a query |
| query | a method of extracting and organising a list of data from a database by incorporating searching, sorting and calculating |
| report | a view of a database used to print out results of a query using a specially formatted layout to display selected attributes |
| data retrieval: complex search | a technique used to extract data that matches more than one criteria |
| data retrieval: complex sort | a technique used to organise data by arranging a number of attributes in ascending or descending order |
| data retrieval: cross table search | a technique used to extract data from a number of related tables |
| data retrieval: calculating | a technique used to produce new data values for each instance in the entity using a mathematical formula based on data in existing attributes |
| data retrieval: summarizing | a technique used to work out values across a number of records such as average, count and sum |
| macro | a sequence of instructions that can be used to automate complex or repetitive tasks - often used in a database to execute a query and print a report based on the results |
| scripted navigation macro | a set of instructions incorporated into a single executable command used to move to another part of the database |
Created by:
MIssRussell
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