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Relational Databases

Higher Info Sys Relational Databases

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