Abstracts are purely summative in nature, usually found in the beginning of scholarly articles, thesis, review, conference proceedings, or any in-depth analysis of a particular subject. They are usually no longer than a paragraph and meant to help the reader quickly understand the text's purpose.
Annotations are more critical summaries of another text and can include information outside of the text itself such as the author's credentials or biases, as well as the text's overall relevance to a larger topic within the scholarship. When part of an annotated bibliography, annotations always contain the citation of the source in a chosen format.
Literature Reviews are the critical summary and synthesis of the current knowledge of a topic. They are meant to be all-encompassing, drawing connections between the key points of published information on the topic.
The meat of an annotated bibliography lies in its annotations. These are brief statements that provide a summary and/or evaluation of a source. Annotations themselves can vary between the following:
Summary annotations provide a concise recap of the source's main points. The two types of summary annotations are informative and indicative. Informative annotations present clear, factual information given by the source, such as thesis, data, and results. Indicative (also called descriptive) annotations give a more broad overview of the source, and do not go beyond describing overall information like topics addressed and/or chapter titles.
Evaluative annotations take a critical look at the source and analyze its usefulness and integrity. Like the name suggests, it evaluates the source with regards to its strengths, weaknesses, and overall relevance to the topic of study and your own paper. In these annotations you can appraise the credibility of the author as well as any biases they may possess.
Combination annotations tend to be the most commonly used in annotated bibliographies. They contain both a brief but detailed summary of the information, as well as a critical analysis of the source as a whole.
The type of annotation you choose to write can depend on the goals of your paper, the needs of your readers, and/or your professor's instructions. Note that when you are writing your annotated bibliography for a class, it is important to adhere to the assignment guidelines outlined by your professor. Some instructions may not clearly state what kind of annotations the assignment requires, so it is advisable to ask for clarification or use your best judgment.