Wirral Part 4 - National Museums Liverpool

Figure 122 Relationship of tables in Access database
Tables
Digitised Details is the main table that holds information on the digitised polygons. It is
directly related to a number of other tables, these tables being either lookup tables or
associated ‘child’ tables.
If the table has an entry related to a lookup table this will be recorded in the table as a
number. This number relates directly to a number in the lookup table that will also
contain text associated with this number. This is the industry standard way of storing
data in a database, it has a number of benefits:
1. It takes up less space – the text only has to be written in the database once and is
represented by a number that takes up less storage space.
2. It is faster – computers perform checks, comparisons etc quick on numbers than
text and there is less volume of data to search through.
3. It reduces errors – we can make sure that a column within our database table can
only contain values that are given in another table, the lookup table. If a value is
entered that is not in this table an error is given. This prevents typos/variations in
longer fields were you can end up with many values meaning the same thing,
which is extremely problematic at analysis time.
4. Easier to maintain – we can add any number of values to the lookup table and
these will automatically be picked up in the application on the form for data entry.
The application only has to scan the small amount of records in this table rather
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