Is there a hypernym for "order confirmation", "quotation" and "invoice"?

With respect, you don't actually want a synonym, you want an abstraction that encompasses the general case. You say as much yourself when you talk about a "base class".

So why not look at what is common in these three things?

Each of them is a communication of information about an order, between two or more parties. Each of them will have a date, a sender, an order reference, and one or more recipients.

Sounds awfully like we are talking about a letter. Or more generally, a communication. Or maybe correspondence.

As a programmer, I'd probably go for something like order-correspondence. Then, when I realise that I also need a class for receipt I've got a ready-made base class.

On the other hand, given such a problem, I'd probably go back to the design board and have a good think about what data I have to deal with, and for what purposes, and hope that having a serious think about the design would lead me naturally to the identification of good entity names.

In other words, if the names aren't obvious, the design probably needs more thought.

Though we can see relations between these three, I doubt you'll find a satisfying synonym to encompass the meaning of all since, similarities aside, they actually do stand for quite different things.

The closest I could posit might be receipt, since each of these have the same property of being received by the person going through the order process.

So, in terms of programming a base class, this could make sense, but I guess we might need more information and a different location to discuss this aspect in much more detail.

How about paper trail?

the records left by a person or organization in the course of activities.

^Wiktionary

• statement sounds to me like the common concept to these, and it has a particular usage in the domain you seem to be covering (business accounting?)

• a good way to look for more general superclass names (in object oriented programming) which is a synonym of hypernym which RegDwight mentioned, is to look in a thesaurus (online or off). Even though a thesaurus is nominally for synonyms (nearby words on roughly the same semantic plane) they tend to give some generalizing terms (hypernyms) and more specific terms (hyponyms), too.

• another good source for such vocabulary is to ask the domain experts. You're probably developing for someone or a group that already has a lot of technical vocabulary about the domain, they will be more likely to have the word that you're looking for. Ask them.