A dissertation is a document that is also known as a thesis and it is what a student turns in as one of the final things to do in order to get a professional qualification. It discusses what you did for research and what you found. This is one of the longest papers you will ever have to write, it normally is made up of several chapters and or sections. It also expresses a lot on a topic you are learning about in your field of subject, it is meant to be very detailed.
In this sense, an abstract is meant to be a synopsis of something that leads to something more. For example, it is like a thesis statement, meant to be short and sweet but to get right to the point, and to just barely mention the whole thing. It is meant to grab your attention to persuade you to keep reading on and to read the whole thing. This is where you pretty much summarize what you are writing about, discuss point you will make and why these points are valid and or more.
When it comes to writing an abstract, it can be a little bit trickier than actually writing the content of the paper itself; this is because the abstract is what will make or break whether or not if the audience will be engaged enough to want to read the whole thing or not. And the point of a dissertation in the first place is to make yourself heard about something that you are passionate about and to make people aware of something fascinating. You can write an abstract in several different ways, some of which include but are not limited to the following: