[I wrote this in 1993 as a letter to a student concerning a draft of his dissertation. in 2003 I edited it to remove some specific references to the student and present it as a small increment to the information available to my grad students. -spaf]
Let me start by reviewing some things that may seem obvious:
- Your dissertation is part of the requirements for a PhD. The research, theory, experimentation, et al. also contribute. One does not attempt to capture everything in one's dissertation.
- The dissertation is a technical work used to document and set forth proof of one's thesis. It is intended for a technical audience, and it must be clear and complete, but not necessarily exhaustively comprehensive. Also note - experimental data, if used, is not the proof - it is evidence. The proof is presented as analysis and critical presentation. As a general rule, every statement in your dissertation must be common knowledge, supported by citation to technical literature, or else original results proved by the candidate (you). Each of those statements must directly relate to the proof of the thesis or else they are not needed.
- The dissertation is not the thesis. One's thesis is a claim - a hypothesis. The dissertation describes, in detail, how one proves the hypothesis (or, rarely, disproves the claim and shows other important results).
Let's revisit the idea of the thesis itself. It is a hypothesis, a conjecture, a theorem. The dissertation is a formal, stylized document used to argue your thesis. The thesis must be significant, original (no one has yet demonstrated it to be true), and it must extend the state of scientific knowledge.
The first thing you need to do is to come up with no more than three sentences that express your thesis. Your committee must agree that your statements form a valid thesis statement. You too must be happy with the statement - it should be what you will tell anyone if they ask you what your thesis is (few people will want to hear an hour presentation as a response).
Once you have a statement of thesis, you can begin to develop the dissertation. The abstract, for instance, should be a one-page description of your thesis and how you present the proof of it. The abstract should summarize the results of the thesis and should stress the contributions to science made thereby.
Perhaps the best way to understand how an abstract should look would be to examine the abstracts of several dozen dissertations that have already been accepted. Our university library has a collection of them. This is a good approach to see how an entire dissertation is structured and presented. MIT press has published the ACM doctoral dissertation award series for over a decade, so you may find some of those to be good examples to read - they should be in any large technical library.
The dissertation itself should be structured into 4 to 6 chapters. The following is one commonly-used structure:
- Introduction. Cover an introduction to the basic terminology, give citations to appropriate background work, briefly discuss related work that has already covered aspects of the problem.
- Abstract model. Discuss an abstract model of what you are trying to prove. This chapter should not discuss any specific implementation (see below)
- Validation of model/proof of theorems. This is a chapter showing a proof of the model. This could be a set of proofs, or a discussion of construction and validation of a model or simulation to be used in gathering supporting data.
- Measurements/data. This would be a presentation of various data collected from real use, from simulations, or from other sources. The presentation would include analysis to show support for the underlying thesis.
- Additional results. In some work there may be secondary confirmation studies, or it might be the case that additional important results are collected along the way to the proof of the central thesis. These would be presented here.
- Conclusions and future work. This is where the results are all tied together and presented. Limitations, restrictions and special cases should be clearly stated here along with the results. Some clear extensions to future work may also be described.
Let's look at these in a little more detail
Chapter I, Introduction. Here, you should clearly state the thesis and its importance. This is also where you give definitions of terms and other concepts used elsewhere. There is no need to write 80 pages of background on your topic here. Instead, you can cover almost everything by saying: "The terminology used in this work matches the definitions given in [citation, citation] unless noted otherwise." Then, cite some appropriate works that give the definitions you need. The progress of science is that we learn and use the work of others (with appropriate credit). Assume you have a technically literate readership familiar with (or able to find) common references. Do not reference popular literature or WWW sites if you can help it (this is a matter of style more than anything else - you want to reference articles in refereed conferences and journals, if possible, or in other theses).