The ES should be no more than about 300 words in length as a maximum. The purpose of the abstract is to provide a brief synopsis of your work, some background, key aim and some synthesis of your findings.
How to write an ES (Dissertation)
Despite the fact that an ES is quite brief, it must do almost as much work as the multi-page dissertation that follows it. Each section is typically a single paragraph. In particular, the parts may be merged or spread among a set of sentences. Use the following as the checklist for your ES:
Why do we care about the problem and the results? If the problem isn’t obviously “interesting” it might be better to put motivation first; but if your work is incremental progress on a problem that is widely recognized as important, then it is probably better to put the problem statement first to indicate which piece of the larger problem you are breaking off to work on. This section should include the importance of your work, the difficulty of the area, and the impact it might have if successful.