Remember that an abstract is basically a short summary of a much longer report. Types of abstracts may be very broadly divided into informative or descriptive abstracts. It will typically highlight the key points which have been covered and will succinctly illustrate the content as well as the scope of the writing. It is meant to reviews the contents in an abridged form.
Descriptive abstracts identify the different areas which are covered in the report. In effect, it is a kind of comprehensive statement of purpose or scope. It indicates the organization of a paper's, not its content. An informative abstract on the other hand will offer a summary of the whole report. That is, it is an overview of the details which are etched out in the actual paper. In general it is about a page long and not over10% of the report.
Descriptive abstracts identify the different areas which are covered in the report. In effect, it is a kind of comprehensive statement of purpose or scope. It indicates the organization of a paper's, not its content. An informative abstract on the other hand will offer a summary of the whole report. That is, it is an overview of the details which are etched out in the actual paper. In general it is about a page long and not over10% of the report.