What is a post coordinate indexing system? Discuss its difference with a pre coordinate indexing systems.

Post-coordinate indexing and pre-coordinate indexing are two distinct approaches used in information retrieval systems to efficiently organize and retrieve information. While each system has its advantages, they differ in terms of their indexing process and search capabilities.

In a post-coordinate indexing system, documents are indexed based on individual terms or descriptors after their creation. Each document is assigned indexing terms separately, and index entries are created by combining these terms. To formulate a query, users combine the desired terms, and the system retrieves relevant documents matching the query.

Flexibility is a key advantage of post-coordinate indexing systems. They allow for highly specific searching, enabling users to combine terms and descriptors in various ways to create complex queries. This flexibility is particularly beneficial in domains with diverse and evolving information needs, such as scientific research or multidisciplinary fields. Moreover, post-coordinate indexing systems efficiently handle large volumes of information as indexing can be performed incrementally with document additions.

On the other hand, pre-coordinate indexing involves combining indexing terms or descriptors before document creation. This system establishes a controlled vocabulary comprising predetermined indexing terms, which are assigned to documents. Each document is represented by a combination of terms, forming an index entry. When users create a query, they select the desired terms from the controlled vocabulary, and the system retrieves documents containing those terms.

The primary advantage of pre-coordinate indexing systems lies in their storage and retrieval efficiency. By using a controlled vocabulary, the number of possible index terms is limited, simplifying the indexing process. This approach enables faster and more accurate retrieval as index entries are predetermined, requiring the system to match selected terms to document representations. Pre-coordinate indexing systems are commonly employed in domains with well-defined and stable vocabularies, such as libraries or specialized databases.

One significant distinction between post-coordinate and pre-coordinate indexing systems is the indexing process. Post-coordinate systems perform indexing after document creation, offering flexibility in selecting descriptors and assigning them to documents. This flexibility facilitates the inclusion of new terms or changes in terminology over time. Conversely, pre-coordinate systems necessitate establishing a controlled vocabulary in advance, which can be time-consuming and challenging to update as new concepts emerge.

Another difference lies in the search process. Post-coordinate indexing systems provide users with greater control over searching by enabling dynamic term combination. Queries can be highly specific and customized to individual information needs. In contrast, pre-coordinate systems restrict search options to the predetermined terms. While this simplicity benefits users with less expertise, it may result in reduced precision and recall if desired terms are absent from the controlled vocabulary.

To summarize, post-coordinate indexing systems offer flexibility and adaptability, making them suitable for domains with diverse and evolving information needs. They allow users to create complex queries by combining terms and support incremental document indexing. Pre-coordinate indexing systems provide storage and retrieval efficiency, making them appropriate for domains with well-defined and stable vocabularies. These systems rely on a predefined controlled vocabulary and offer a simpler search process with predetermined index terms. The selection of an indexing system depends on the nature of the information domain and the specific requirements of users.