CODEWITHSUNDEEP
oopdatabase-designms-access-2013
Superbest
Superbest

Reputation: 26612

Object oriented model for tables in MS Access

I have an MS Access database with several tables. Almost all tables contain inventory information about different classes of items (there are some utility tables which store extra information, such as a list of classes and lists of commonly used lookup values). Some classes of items have particular data specific to them - for instance, volume is relevant for liquids but not solid objects, but all objects have a location. The logical structure of my database is a textbook example of a case where an object oriented model provides clarity and maintainability benefits:

Let's say my dates are currently displayed as MM/DD/YYYY. I want to change them to ISO format (YYYY-MM-DD). Currently, I have to open every single table I have (about 20) and change the format in each one of them one by one. If there was some kind of inheritance mechanism, I could instead change the format only in my top-level InventoryTable, and all my other tables would inherit the change.

Or, suppose I decide to store a new piece of data, called "Owner", for all items. This would describe who entered the item into the inventory. I could simply add this column to InventoryTable, and it would appear in all the child tables automatically.

Lastly, let's say I make cosmetic changes such as rearranging the order of columns. Let's say in my document-related tables, the page number appeared at the end. I instead move the page number to the very beginning of the table - this would propagate to both DocumentTable as well as LetterTable but not unrelated tables.

Bear in mind that I am editing these tables manually using the GUI of MS Access 2013. When editing information pertaining to a single class of items, I would not like to switch back and forth between tables or queries to edit different parts of the same record - I want to be able to see and edit all of the information for any given record in one place. Therefore, some complicated solutions based on chaining queries may be impractical.

Is it possible for me to accomplish what I want (the inheritance structure) in Access using some kind of object oriented scheme? Is there an alternative way of obtaining the same benefits? Do I have no choice except to give up and manually propagate every change to all tables?

Upvotes: 0

Views: 1767

Answers (2)

Walter Mitty
Walter Mitty

Reputation: 18940

The relational data model does not have inheritance built in. There are several design patterns that allow the database designer to mimic the behavior of inheritance in a system of relational tables. Two common designs are known as "Single Table Inheritance" and "Class Table Inheritance". There are two tags in this area with questions that relate to these two techniques, and a brief description in the info under the tag. With one of these two techniques, you will be able to model a superclass/subclass situation.

For a more complete description, you could search for Martin Fowler's treatment of the two techniques on the web. There is a third technique, called "Shared Primary Key" which allows you to enforce the one-to-one nature of the IS-A relationship between members of the subclasses and members of the superclass.

Your big problem in MS Access is going to be implementing the code that these techniques leave to the application programmer. Get ready to do plenty of coding in VBA, and tying this code to the user's dashboard.

Upvotes: 1

Sam Hobbs
Sam Hobbs

Reputation: 2891

It is not possible to make tables in Access object-oriented because it is not possible to directly associate methods with tables. An object is defined to be both properties and methods. Access is not designed to do that.

Also note that Access is not the best that Microsoft has to offer. You will get more power and capabilities with SQL Server.

Upvotes: 1

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