The results of queries are displayed in
An entity is made up of a number of
With this data type you are given a choice of two entries for a data item, for example true or false, yes or no, male or female.
defined by the relationships between data entities. This explains how each entity links to another. There are three types of cardinality/relationship: one-to-one, one-to-many and many-to-many.
Performing search criteria on one or more fields for example on surname and date of birth fields. This could be across more than one table if linked in a relational database through primary and foreign keys.
A primary key made up of two or more attributes.
Special data type that allows you to store dates in various different formats, for example short date dd/mm/yy.
may be set to give boundaries to the data domain.
Data deletion problems
If a record is removed from a flat file database you may not want to remove the entire contents of the record but there is no way of only removing part of it ,therefore you have ?????
This can be can be thought of as meta data: data about data. This lists the attributes of an entity and the properties for each attribute. The main properties listed are attribute name, data type, size validation and an indication of primary or foreign key.
Refers to all the unique values which a data element may contain. For example a field for gender may contain M or F only.
Making sure that each data item is stored only once in a database.
Represents one thing, a person or object.
Data insertion problems
There is normally no way of entering only part of the flat file database. For example, with a library member, details might be stored only once a person borrows a book so there would be no way of storing the person's details if they haven't borrowed a book yet.
Enforced in a database system by a series of integrity rules. This makes sure data are consistent and correct. The types of integrity constraints used within a relational data model are entity integrity and referential integrity.
Used to describe how data is represented and stored. The data model is in first normal form (1NF) if it has no multi-valued attributes. The data model is in second normal form (2NF) if it is in 1NF and there are no partial dependencies. The data model is in third normal form (3NF) if it is in 2NF and there are no non-key dependencies.
This is the process of defining entities, attributes and relationships. The result is called a data model.
Data modification problems
If you want to update a person's details on a flat file system you may have to update every time the details are used in the database, leading to possible mistakes and ...........
Each attribute in a database must have a particular ..........
Every entity must have a primary key. This should be a unique value and can not be a null value; it cannot be left blank.
Entity relationship diagram
These diagrams show how the entities that make up a relational database are linked together. Using cardinality the relationships are displayed using a straight line to link the entities, which are represented by a rectangle.
First normal form
to remove repeating groups by creating a new entity.
an attribute in one entity and a primary key in another entity. It is used to form a relationship and is always on the many side. This key must have the same data type as the corresponding primary key.
Used to hold whole numbers, for example 3, 1234, 0, -5.
Reference to a file by linking to a file outwith the database, for example object linking and embedding.
feature of a relational database that is used to ensure referential integrity. You can lookup a value for one attribute from another, for example you can lookup the values for a foreign key from a primary key.
Many to many relationships
can be thought of as a connection between two entities where many occurrences on one entity are related to many occurrences in another entity. For example, in a library each book can be borrowed by many members and each member can borrow many books, giving a many-to-many relationship between members and books.
should only be used as a key if it can be guaranteed not to change.
An attribute that has more than one value stored within it.
This occurs when attributes do not depend on the primary key.
process used to try to remove insertion, update and deletion anomalies. A relational database can be described as normalised if it is in third normal form (3NF). 3NF tables should not have insertion, update and deletion anomalies.
This occurs when an attribute is left blank. A primary key can never have this.
A file created using another application program, for example a picture or sound file or a word-processed document.
One to one relationship
connection between two entities where one entity is related to one occurrence in another entity. For example, one student can only have one locker, giving a ?????? relationship.
One to many relationship
connection between two entities where one entity is related to many occurrences in another entity. For example, in a class one teacher teaches many students, giving a ????? relationship.
Partial key dependency
This is where attributes depend on only part of a compound/concatenated key.
This validation rule specifies if an attribute can be left blank or if it must contain a value.
uniquely identifies each instance in an entity. It is used to form a relationship and is always on the one side.
These are used to allow users to search, sort and perform calculations on the stored information.
This validation rule specifies if an attribute must be between a certain range of values, for example a number must be entered between 1 and 10. No other value is allowed.
Real data type
This is used to hold numbers with decimal points, for example 3.14, 1234.0, -5.2
ensures consistency between linking of tables through primary and foreign keys. For a relationship to work correctly the properties defined in the data dictionary for each matching primary and foreign key must be the same, for example they must be of the same data type, size and validation. This means any attribute in an entity that is a foreign key can only contain values from the primary key.
This is where more than one value is stored within an attribute.
This validation rule specifies a list from which a choice can be made to fill a value into an attribute. This may be a person's title, for example Mr, Mrs, Miss, Ms.
Second normal form
to remove partial dependency. That means to remove attributes that are only dependent on part of the primary key. This only applies to entities where the primary key is made up of two or more attributes (compound/concatenated key). Attributes which are uniquely described by only part of a compound/concatenated key are said to be partially dependent on the primary key. You need to move the partially dependent attributes to a new entity along with the part of the compound/concatenated key they are dependent on. This part of the key is then a foreign key in the original entity and the primary key in the new entity.
a sequence of instructions that can be used to automate complex or repetitive tasks
normally record a sequence of events and are then stored and reused.
small programs that can be developed within an application package.
An attribute that has only one value stored within it.
If there is no unique key or there would be too many attributes in a compound key then a unique identifier may be made up
can hold a combination of letters and numbers.
Third normal form
to remove attributes that do not depend on the primary key. This means that if an attribute can be derived from another attribute then it can be removed to a new entity. You remove the non-key dependency by removing the attributes, and the non-key field they are dependent on, into a new entity, and making the determinant field the primary key. The non-key field then becomes a foreign key in the original entity.
This is a special data type that allows you to store time in various different formats, for example hh:mm:ss.
data in a form that has repeating groups and has not been normalised.
the process of checking if an attribute satisfies certain specified rules. The rules may include a presence check, range check or restricted choice.