Any application software keeps track of certain kinds of information over time. Identifying the main objects of information and the facts associated with those objects helps determine what information needs to be kept. To keep track, a list of all the items of information is prepared. It is convenient to organize this detailed information into tables. A single table lists the facts related to a single object of information. It describes a general plan for the specific data that is stored as a record. Each information fact, or field, may have certain attributes associated with it, such as the size of the item, or whether the item is text or a number, etc
It is necessary to list the tables of information that need to be stored. This is important for the programmer to be able to create the applications database. And it is important to the customer to be sure that all the necessary information is available to the application software.
Information takes up space. Storage formats represent the space that a certain piece of information consumes. For example, the word zebra takes five alphabetic characters. The storage format for this word is (A5), where A indicates an alphabetic data type and 5 is the maximum number of characters allowed. Here are some examples of some other similar storage formats:
The storage format indicates what kind of information (text, numbers, dates, etc.) is stored. It also shows how much space is reserved for an item of information. It is important to make sure that there is enough space for the largest value that might be encountered. If there is not enough space to contain the item, the system will malfunction.
Besides just being able to store letters, numbers, and symbols using the A storage format, there is a numerical storage format for just numbers. This is the N storage format. Here are some examples:
The first example limits the currency to three numbers, a decimal point, and two decimal places. The maximum number that could be stored using such a storage format is 999.99.
The second example can only accept four numbers. The maximum number that could be stored is 9999. If the process needed to weigh a large truck weighing 25,000 pounds, the (N4) storage format would be too small and would need to be increased to (N5).
There are other storage formats possibly used in this document:
The storage formats mentioned here are a generic subset common to many of todays development environments.
This design utilizes a table naming convention similar to the Leszynski/Reddick Guidelines for naming conventions in Access database design. Table names consist of the tag tbl concatenated with the table description. The intention for table descriptions is to make them highly readable, which excludes abbreviations in most cases. There are no spaces between field name parts and multiple words are delimited via capitalization.
Nominal record length is calculated by summing up the length of the fields. A memo can contain 0 64,000 bytes for each instance of a memo field, but memos are rarely this large in practice. An representative value is chosen which is considered typical for the use in the record. The size of a memo field is calculated as 10 (for the link to the memo) plus the representative size of the memo contents. Index size per record is calculated as the size of indexed field (s) plus a 10 byte link per indexed field.
