# Introduction {% embed url="" %} Project Source @ Github {% endembed %} [RecallGraph](https://github.com/RecallGraph/RecallGraph) is a *versioned-graph* data store - it retains all changes that its data (vertices and edges) have gone through to reach their current state. It supports *point-in-time* graph traversals, letting the user query any past state of the graph just as easily as the present. It is a [Foxx Microservice](https://www.arangodb.com/why-arangodb/foxx/) for [ArangoDB](https://www.arangodb.com/) that features *VCS-like* semantics in many parts of its interface, and is backed by a transactional event tracker. It is currently being developed and tested on ArangoDB v3.5 and v3.6, with support for v3.7 in the pipeline. **Example:** [**A Time-Travelling Mind Map Tool**](https://hivemind.vercel.app/)**.** [![Build Status](https://travis-ci.org/RecallGraph/RecallGraph.svg?branch=development)](https://travis-ci.org/RecallGraph/RecallGraph) [![Quality Gate Status](https://sonarcloud.io/api/project_badges/measure?project=adityamukho_evstore\&metric=alert_status)](https://sonarcloud.io/dashboard?id=adityamukho_evstore) [![Coverage](https://sonarcloud.io/api/project_badges/measure?project=adityamukho_evstore\&metric=coverage)](https://sonarcloud.io/component_measures?id=adityamukho_evstore\&metric=coverage) [![Maintainability Rating](https://sonarcloud.io/api/project_badges/measure?project=adityamukho_evstore\&metric=sqale_rating)](https://sonarcloud.io/dashboard?id=adityamukho_evstore) [![Reliability Rating](https://sonarcloud.io/api/project_badges/measure?project=adityamukho_evstore\&metric=reliability_rating)](https://sonarcloud.io/dashboard?id=adityamukho_evstore) [![Security Rating](https://sonarcloud.io/api/project_badges/measure?project=adityamukho_evstore\&metric=security_rating)](https://sonarcloud.io/dashboard?id=adityamukho_evstore) ## Do I Need a 'Versioned Graph' Database? To get an idea of where such a data store might be used, see: 1. [The Case for Versioned Graph Databases](https://adityamukho.com/the-case-for-versioned-graph-databases/), 2. [Illustrative Problems in Dynamic Network Analysis](https://en.wikipedia.org/wiki/Dynamic_network_analysis#Illustrative_problems_that_people_in_the_DNA_area_work_on) Also check out the recordings/slides below: {% embed url="" %} RecallGraph presented @ ArangoDB Online Meetup {% endembed %} {% embed url="" %} The associated slide deck {% endembed %} {% embed url="" %} A discussion on RecallGraph's development roadmap {% endembed %} {% embed url="" %} The associate slide deck {% endembed %} **TL;DR:** RecallGraph is a potential fit for scenarios where data is best represented as a network of vertices and edges (i.e., a graph) having the following characteristics: 1. Both vertices and edges can hold properties in the form of attribute/value pairs (equivalent to JSON objects). 2. Documents (vertices/edges) mutate within their lifespan (both in their individual attributes/values and in their relations with each other). 3. Past states of documents are as important as their present, necessitating retention and queryability of their change history. ## API Features RecallGraph's API is split into 3 top-level categories: ### Document * **Create** - Create single/multiple documents (vertices/edges). * **Replace** - Replace entire single/multiple documents with new content. * **Delete** - Delete single/multiple documents. * **Update** - Add/Update specific fields in single/multiple documents. * **Restore** - Restore deleted nodes back to their last known undeleted state. * **(Planned) Materialization** - Point-in-time checkouts. * **(Planned) CQRS/ES Operation Mode** - Async implicit commits. ### Event * **Log** - Fetch a log of events (commits) for a given path pattern (path determines scope of documents to pick). The log can be optionally grouped/sorted/sliced within a specified time interval. * **Diff** - Fetch a list of forward or reverse commands (diffs) between commits for specified documents. * **Explicit Commits** - Commit a document's changes separately, after it has been written to DB via other means (AQL / Core REST API / Client). * **(Planned) Branch/Tag** - Create parallel versions of history, branching off from a specific event point of the main timeline. Also, tag specific points in branch+time for convenient future reference. ### History * **Show** - Fetch a set of documents, optionally grouped/sorted/sliced, that match a given path pattern, at a given point in time. * **Filter** - In addition to a path pattern like in **'Show'**, apply an expression-based, simple/compound post-filter on the retrieved documents. * **Traverse** - A point-in-time traversal (walk) of a past version of the graph, with the option to apply additional post-filters to the result. * **k Shortest Paths** - Point-in-time, weighted, shortest paths between two endpoints. * **Purge** - Delete all history for specified nodes. ## Limitations 1. Although the test cases are quite extensive and have good coverage, this service has only been tested on single-instance DB deployments, and **not on clusters**. 2. As of version 3.6, ArangoDB does not support ACID transactions for multi-document/collection writes in [cluster mode](https://www.arangodb.com/docs/3.6/transactions-limitations.html#in-clusters). Transactional ACIDity is not guaranteed for such deployments. ## Development Roadmap 1. Support for absolute/relative revision-based queries on individual documents (in addition to the timestamp-based queries supported currently), 2. Branching/tag support, 3. Support for the *valid time* dimension in addition to the currently implemented *transaction time* dimension (), 4. Support for ArangoDB v3.7, 5. Multiple, simultaneous materialized checkouts (a la `git`) of selectable sections of the database (entire DB, named graph, named collection, document list, document pattern), with eventual branch-level specificity, 6. CQRS/ES operation mode (async implicit commits), 7. Support for ArangoDB clusters (limited at present by lack of support for multi-document ACID transactions in clusters). 8. Multiple authentication and authorization mechanisms. ## Get in Touch * Raise an issue or PR on the [project repository](https://github.com/RecallGraph/RecallGraph), or * Mail me () or * Join the [Gitter channel](https://gitter.im/RecallGraph/community). {% hint style="warning" %} ## :no\_entry\_sign:Disclaimer The authors and maintainers of RecallGraph are not liable for damages or indemnity (express or implied) for loss of any kind incurred directly or indirectly as a result of using this software. {% endhint %}