Choosing a static dictionary technique is most appropriate when considerable prior knowledge about the source is available. This technique is especially suitable for use in specific applications. For example, if the task were to compress the student records at a university, a static dictionary approach may be the best. This is because we know ahead of time that certain words such as “Name” and “Student ID” are going to appear in almost all of the records
Other words such as “Sophomore,” “credits,” and so on will occur quite often. Depending on the location of the university, certain digits in social security numbers are more likely to occur.
For example, in Nebraska most student ID numbers begin with the digits 505. In fact, most entries will be of a recurring nature. In this situation, it is highly efficient to design a compression scheme based on a static dictionary containing the recurring patterns. Similarly, there could be a number of other situations in which an application-specific or data-specific static-dictionary-based coding scheme would be the most efficient. It should be noted that these schemes would work well only for the applications and data they were designed for. If these schemes were to be used with different applications, they may cause an expansion of the data instead of compression