5.3. Split Mongo Modulestore


5.3.1. Overview

Split Mongo is the term used for the new edX modulestore. Split Mongo is built on mongoDB. For information about mongoDB, see the mongoDB website.

The “split” in Split Mongo refers to how a course is split into three types of information:

  • The course identity, referred to as the course index
  • The course structure
  • The course content, referred to as XBlock definitions.

This separation of identity, structure, and content enables course authors to use more advanced capabilities when developing and managing courses.

5.3.2. Split Mongo Data Model

In the Split Mongo data model, edX courses are split into three collections: Course Index

The course index is a dictionary that stores course IDs. Each course ID points to a course structure.

The course index supports multiple branches of a course. The index can store multiple entries for a course ID, with each entry pointing to a different course structure that corresponds to a different branch.

As currently implemented, for each course, there is a branch for both the published and draft versions of the course. The published and draft branches of the course point to different structures.

In the edX Platform:

  • Students using the LMS see and interact with the published version of the course.
  • Course team members using edX Studio make changes to the draft version of the course.
    • When the user changes a the course outline, display names, the course about page, course updates, other course pages, sections or subsections, the draft branch is automatically published; that is, it becomes the published branch.
    • For units and components, changes are saved in the draft branch. The user must publish the unit to change the draft branch to the published branch. When the user begins another set of changes, the draft branch is updated. Course Reruns

The edX Platform enables you to rerun a course. When you rerun a course, a new course index is created. The new course index points to the same course structure as the original course index. Course Structures

The course structure defines, or outlines, the content of a course.

A course structure is made up of blocks in a tree data structure. Blocks are objects in a course, such as the course itself, sections, subsections, and units. A block can reference other blocks; for example, a section references one or more subsections. Each block has a unique ID that is generated by the edX Platform.

Each block in the course structure points to an XBlock definition. Different blocks, in the same or in different structures, can point to the same definition.

Course structures, and each block within a structure, are versioned. That is, when a course author changes a course, or a block in the course, a new course structure is saved; the previous course structure, and previous versions of blocks within the structure, remain in the database and are not modified. XBlock Definitions

XBlock definitions contain the content of each block. For some blocks, such as sections and subsections, the definition consists of the block’s display name. For components, such as HTML or problem components, the definition also contains the content of the object. A definition can be referenced by multiple blocks.

XBlock definitions are versioned. That is, when a course author changes content, a new XBlock definition for that object is saved; the previous definition remains in the database and is not modified.

5.3.3. Split Mongo Capabilities

The Split Mongo data model enables the edX Platform to implement advanced content management functionality. Specifically, Split Mongo is designed to enable:

While these capabilities are not fully implemented in the edX Platform, Split Mongo is designed to allow future enhancements that enable these content management capabilities. Multiple Course Branches

Split Mongo enables multiple branches of a course. The course index <Course Index>_ can have multiple entries for a course ID, each of which points to a different structure.

The edX Platform currently uses a draft and a published branch for a course. Future enhancements may use other branches. Versioning

In Split Mongo, every change to a course or a block within the course is saved, with the time and user recorded.

Versioning enables future enhancements such as allowing course authors to revert a course or block to a previous version. Content Reuse

By using pointers to reference XBlock definitions from course structures, Split Mongo enables content reuse. A single XBlock definition can be referenced from multiple course structures.

Future enhancements to the edX Platform can allow course authors to reuse an XBlock in multiple contexts, streamlining course development and maintenance.