Data model for projects

Date: 17/04/2018

Status

Accepted

Context

We need to define how to save and query project, subproject and workflow data efficiently.

Definition of terms

• Project: Is the root element of the hierarchy. It contains metadata and Subprojects
• Subproject: Are a subset of Projects and collect a number of Workflowitems
• Workflowitems: Are a number of steps which need to be executed in a certain order
• Resources: Projects, Subprojects, Workflowitems are resources. This means they contain permissions, a log and metadata.

Relations

graph TD;
    Project-->Subproject_A;
    Project-->Subproject_B;
    Subproject_A-->Workflowitem_A;
    Subproject_A-->Workflowitem_B;
    Subproject_B-->Workflowitem_C;
    Subproject_B-->Workflowitem_D;

Options

1. Each resource has its own stream. Each resource has an array which links to the underlying resources (e.g. A Projects has an array of the ids of its Subrojects). That means if we want to query Subprojects of a specific Project, we need to lookup the Subproject ID's inside the projects to afterwards fetch all the underlying Subproject streams. Pro: We are only fetching the data which is necessary, changes inside the resources are storage efficient. Con: Resources with a high number of relations result in multiple (maybe hundreds) of queries.
2. Each Project has its own stream. All relational resources of the projects are stored inside a JSON and resolved on the API Layer. Pro: Only one query necessary to resolve the whole resource tree for one project. Con: Large amount of storage needed, since every change inside a single resource would trigger a whole copy of the project tree. Large data structures have to be kept in memory
3. Each project has its own stream. All relational resources are organized with multiple key-items inside the project stream. This allows to specifically query resources with a single query. Updates to resources will only result in the copy of the affected resource. Pro: Easy to query, low storage / memory footprint Con: None

Decision

Since we need to be able to scale out to larger projects, it is important to be able to execute fast queries and having a low storage / memory footprint. The goal is to exploit the Multichain API as much as possible, since we can expect it to be more performant than our API. Option 3 is the option, which covers the required capabilities in the best way.

Implementation

Each project will have its own stream. It contains its own resources specific metadata inside specific keys (e.g. _logs, _permissions, _metadata). All underlying resources will be stored with specific key arrays.

Keys	Resource
"_log"	Changelog of the project
"_permissions"	Permissions of the project
"_metadata"	Details of the project
["subprojects", "<id of subproject>"]	Subproject
["<id of subproject>_workflows", "<id of workflow>"]	Workflow

To efficiently query the resources we can execute the following commands:

Action	Command
Get project details
List all subprojects	liststreamkeyitems projectx subprojects
Get specific subproject details	liststreamkeyitems projectx tenderxyz
List workflows	liststreamkeyitems projectx tenderxyz_workflows
Get specific workflow details	liststreamkeyitems projectx workflowxyz

Consequences

With this solution we have a minimal amount a calls and fast retrieval of resource data. Performance tests need to be executed but we expect this method to scale well when the amount of resources grows