I don't know much but here are some of my understanding, A tModel is kind of a template to describe specifications regarding the characteristic of, a say web service, an entity. these templates are typed with tModel as the super type of all the tModel. One usually should able to look at what tModel is assoicated with a business service to tell what KIND of servce and look at the tModel instance details to see neccessary infos to use the servce. You can define your one tModel and tModel can be asssionated with "a log of " data sturectres to make your regdata store more info in a agreed way. I wish I did not create more confustion.
From the spec, it clarifies this very well for where we usually use tModel: There are two places within a businessEntity registration that you�ll find references to tModels. In this regard, tModels are special. Whereas the other data within the businessEntity (e.g. businessService and bindingTemplate data) exists uniquely with one uniquely keyed instance as a member of one unique parent businessEntity, tModels are used as references. This means that you�ll find references to specific tModel instances in many businessEntity structures. 1.Defining the technical fingerprint The primary role that a tModel plays is to represent a technical specification. An example might be a specification that outlines wire protocols, interchange formats and interchange sequencing rules.
2.Defining an abstract namespace reference The other place where tModel references are used is within the identifierBag, categoryBag, address and publisherAssertion structures that are used to define organizational identity and various classifications. Used in this context, the tModel reference represents a relationship between the keyed name-value pairs to the super-name, or namespace within which the name-value pairs are meaningful.