Ed-Fi API resources have two overlapping key systems. This section describes the structure of the different systems along with detail about how and in what circumstances API clients interact with each.

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Resource IDs

In the API, Ed-Fi API resources are assigned a resource ID by the API implementation. The identifiers could be generated using a UUID (universally unique identifier) implementation like Microsoft's GUID (globally unique identifier), this identifier should be generated by the Ed-Fi API and not assigned from an external source and it will never change.

This ID helps provide for compatibility with REST conventions. For example, a CourseOffering can be looked up/queried by doing a HTTP GET on a path like this:

/courseOfferings/d0fd729db6ee4a7bbc989720e4f833f5

In the JSON, the resource ID appears as the "id" element

Figure 1: the resource ID in the JSON.

The resource ID is API assigned and can't be requested.  Further, if a HTTP POST includes such an ID that ID will either be ignored or result in an error - in either case, it should not be included!

Natural Keys

To improve data quality and maximize the possibility for data to move between systems, an Ed-Fi APIs data model also employs a natural key system.

The key for an entity can be looked up by using the either the Unifying Data Model - v4.0 Handbook or the Unifying Data Model - v5.0 Handbook and looking under the column “Identity” – key fields are indicated there. For example, for the CourseOffering entity, this page appears:

Figure 3: natural key fields are shown by looking at the "identity" column in the UDM Handbook.

You can see that the entity has three keys: a LocalCourseCode, a School, and a Session. Collectively, these constitute the natural key.

In the API for the /courseOffering (you can see this resource in the Ed-Fi ODS API Sandbox), the JSON reveals that these keys collectively contain 4 fields, as the Session has 3 fields in its natural key:

Figure 4: JSON snippet for CourseOffering

So the key for CourseOffering is constituted by these fields:

• schoolId
• schoolYear
• termDescriptor
• localCourseCode

Why does Ed-Fi use composite natural keys instead of only assigning entities a surrogate ID and using that exclusively? The use of ecosystem identifiers plays two important roles, explained below.

Allow systems with no knowledge of the API to transact with the API

If the API assigns all keys, then systems with no knowledge of the API are at a distinct disadvantage. In the case above, you can see that a system that has the school, session, and course code would be easily able to locate and query this entity. All of the key fields here are often well-known within the K-12 district already.

Support key field unification to improve data quality

Note in the JSON above that schoolId appears twice, but we only list it once as part of the key. Why is that? The reason is that the API "unifies" the schoolId that is part of the SchoolReference and the SessionReference. If an API tries to POST a CourseOffering where those two schoolIds differ, the API will refuse the transaction as these fields are unified by the API. This ensures a basic level of data integrity – that the CourseOffering being created at a School is assigned to a Session that is also part of that School.

Detecting Key Field Merges

How do you know when fields are being unified? This information is declared in the Ed-Fi Data Handbook under the Merge column.

Figure 5: the "Merge" column shows which fields in the entity are merged - this merging is most common with key fields.

1. Note that the Ed-Fi ODS API v2.x allows for resource IDs to be chosen by clients; this functionality is deprecated and is removed in the ODS API v3 and beyond.