The current Ed-Fi community has struggled with the non-longitudinal nature of many "indicators" in the model. For the purposes of this analysis, an "indicator" is generally regarded as a field describing an important characteristic of a primary data model entity (e.g. a student, school, etc.). Also, for the purposes of this analysis, indicators will have a very broad definition: the value of an indicator can be binary in nature (true/false) or have a value associated with them ("red", "not submitted", "3.3", etc.).
Historically, there have been a 2 important use cases relating to indicators:
Use Case 1: as an agency performing data collections and reporting, I want to capture the value of a indicator for a period of time or at a moment in time (e.g. at the end of a month) so I can perform operations such as issuing payments to districts or performing state reporting.
Use Case 2: as a school district, I want to track the movement of indicators over time so I can make instructional decisions on how to intervene to improve the education of the student.
The longitudinal nature of indicators is important in case #2, but not in case #1. The evolution of Ed-Fi has also meant that many indicators only support case #1.
The obvious solution is to add dates, but due to the natural key system of Ed-Fi, the adding of dates is not straightforward. To take a very simple example, consider this data model; this not Ed-Fi today, but it illustrates the problem: