Object Oriented Databases Message Class
Message Class: Basic Attributes The message class will have the following attributes:
Message Format and References: Another attribute might be “format”. Rather than simply define this as an integer and assign different formats a unique number, let’s create a new class “Format” and refer to the message’s format using a reference.
There are currently many different formats for messages and there will be many more created in the future. For e-mails, the standards are defined by different “Request for Comment” documents called RFCs. One of the original baselines was RFC822, but there have been many new RFC documents that are new versions of the format.
By defining a class called format, we can include the attributes that are common and stable (if any) over all the versions and use this as a base class. We can then define specific formats and add new attributes by deriving new classes from the base class.
As new formats are created, we can either create a new instance of an existing format with different attribute values or we create a whole new class derived from Format if no existing formats fit.
Unlike SQL tables, the object-oriented approach gives us the flexibility to fit the data structures to the existing structures that already exist and also be adaptable to new structures that may be defined.
If we simply assigned a number that matched an entry in a format table, we’d have to assume that the SQL query would include knowledge of the table(s) to search to find that entry (in the FROM clause). By using a reference, we can go directly to the format object, regardless of what specific type of format it is. Changes to the schema are less likely to require changes to the data.