Database Background Information.

The following is of a technical nature but should serve as background information about the nature of a relational database and how it relates to this application. 

One of the important features of a relational database that permits using a single table, like the one depicted here as CornContract is SQL Server's underlying ability to maintain the integrity of the relationships between data in one table with that of another's.

The term generally used for this ability is called "Referential Integrity". The key to the CornContract table"s significance, aside from the information it carries, is the relationship that information has to other tables and the guarantee that it refers to one and only one entry in another table where a positive identity is called for. 

The methodology that has been applied to the example below is based on a person or company being responsible for all the components involved and maintaining a 1:1 correspondence between people and components. 

The rules that have been set up in this case insist that either a vendorID or a growerID exist for all items and events in the system. No seed can be entered,  no plot of land or other asset can be added to the system without there being a unique ID for the person responsible pre-existing in either the Grower or Vendor tables..  

Additionally, each time  a CornContract entry is made, the system checks to see that the entry for the critical line items (numbered 1,2 and 3 respectively in the charts below) exist in the other tables. This system of checks work both ways. You cannot, for instance delete a seed entry if there is an active CornContract in place using that seed. You would not be able to delete a truck, barge or railcar if it was currently carrying a load listed in the active contract list either.

This system of rules imposes some limitations on how items are entered into the database, but they all support the system's integrity. You could not just give a load to a truck driver and "do the paperwork later" and have him listed in the system. You must first:

• Enter the owner of the truck in the vendor table,

• Enter the truck in it's proper table.

• Only then can the entry be made that marks a portion of that contract as being in that truck.

A database is not just the many tables that make up its data, it is the interlocking system of rules that govern the relationships between the different tables as well.  (a more complete map of these relationships can be seen by clicking on the Map button on the left)

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