{"id":1226,"date":"2023-04-13T15:26:42","date_gmt":"2023-04-13T14:26:42","guid":{"rendered":"https:\/\/blogs.glowscotland.org.uk\/es\/software\/?page_id=1226"},"modified":"2023-08-28T10:11:41","modified_gmt":"2023-08-28T09:11:41","slug":"database-design","status":"publish","type":"page","link":"https:\/\/blogs.glowscotland.org.uk\/es\/software\/data-modelling\/database-design\/","title":{"rendered":"Database design"},"content":{"rendered":"\n

Entity relationship diagrams<\/h2>\n\n\n\n

In entity relationship diagrams the tables are drawn with lines connecting them to show relationships.<\/p>\n\n\n\n

They can either be simple, just showing the table name:<\/p>\n\n\n

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\"Example
Example of a simple entity relationship diagram from BBC Bitesize<\/figcaption><\/figure><\/div>\n\n\n

Or more complex, listing the attributes within the table:<\/p>\n\n\n

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\"Example
Example of a more complex entity relationship diagram from BBC Bitesize <\/figcaption><\/figure><\/div>\n\n\n

In either case, the important part of the design is the line connecting the tables. This represents the type of relationship between them.<\/p>\n\n\n\n

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Entity occurrence diagrams<\/h2>\n\n\n\n

An entity-occurrence diagram shows the relationship between occurrences of entities. In other words specific entries in a table rather than the table as a whole.<\/p>\n\n\n\n

Each table is shown as a tall oval. Each occurrence of an entity is show by a dot and a description.<\/p>\n\n\n

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\"Example
Example of an entity occurrence diagram from BBC Bitesize <\/figcaption><\/figure><\/div>\n\n\n
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One-to-one relationship<\/h2>\n\n\n\n

A one-to-one relation occurs when an entity in one table is only ever related to a single entity in another table and vice versa. It can be represented in either of the following ways:<\/p>\n\n\n\n

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\"Example
Example of one-to-one shown as an entity relationship diagram <\/figcaption><\/figure><\/div><\/div>\n\n\n\n
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\"Example
Example of one-to-one shown as an entity occurrence diagram<\/figcaption><\/figure><\/div><\/div>\n<\/div>\n\n\n\n
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One-to-many relationship<\/h2>\n\n\n\n

A one-to-many relation occurs when an entity in one table can be related to multiple entries in another table. It can be represented in either of the following ways:<\/p>\n\n\n\n

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\"Example
Example of one-to-many shown as an entity relationship diagram<\/figcaption><\/figure><\/div><\/div>\n\n\n\n
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\"Example
Example of one-to-many shown as an entity occurrence diagram<\/figcaption><\/figure>\n<\/div>\n<\/div>\n\n\n\n
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Many-to-many relationship<\/h2>\n\n\n\n

A many-to-many relation occurs when an entities in one table can be related to multiple entries in another table and vice versa. It can be represented in either of the following ways:<\/p>\n\n\n\n

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\"Example
Example of many-to-many shown as an entity relationship diagram<\/figcaption><\/figure><\/div><\/div>\n\n\n\n
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\"Example
Example of many-to-many shown as an entity occurrence diagram<\/figcaption><\/figure><\/div><\/div>\n<\/div>\n\n\n\n
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Data dictionaries<\/h2>\n\n\n\n

Data dictionaries are used to define the structure of a database.<\/p>\n\n\n\n

Data dictionaries contain the following:<\/p>\n\n\n\n