Begin of the insertion# Data architecture for hierarchical attributesEnd of the insertion Begin of the deletion ### RequirementsEnd of the deletion

Begin of the insertion## Context and Problem Statement

What is the data architecture for serving a hierarchy of tag with associated metadata to an OpenProject custom field implementation?

## Decision Drivers

End of the insertion * The Begin of the insertiondata architecture needs toEnd of the insertion structure Begin of the insertiontags in a hierarchical way (like a tree), where each tag has associated metadata.

* The structure can change at any point in time.

* Changes to the structure need to be recorded throughout the life-time.

* The data architectureEnd of the insertion must be Begin of the insertioncapable to be used for filtering based on given tags.

* When the hierarchical structure changes, it must be possible to update pointers to it (the custom field).

* When the hierarchical structure changes, it must be possible to to let pointers point to "older" versions of the structure.

* Changes to the structure must be auditable.


## Considered Options

* Event sourced structure

* Using paper trails

* No historic data is captured


## Decision Outcome

Chosen option: "{title of option 1}", because {justification. e.g., only option, which meets k.o. criterion decision driver | which resolves force {force} | … | comes out best (see below)}.

### Consequences

* Good, because {positive consequence, e.g., improvement of one or more desired qualities, …}

* Bad, because {negative consequence, e.g., compromising one or more desired qualities, …}

* …


### Confirmation

{Describe how the implementation of/compliance with the ADR is confirmed. E.g., by a review or an ArchUnit test. Although we classify this element as optional, it is included in most ADRs.}

## Pros and Cons of the Options

### Event sourced structure

{example | description | pointer to more information | …}

* Good, because {argument a}

* Good, because {argument b}

* Neutral, because {argument c}

* Bad, because {argument d}

* …


### Using paper trails

{example | description | pointer to more information | …}

* Good, because {argument a}

* Good, because {argument b}

* Neutral, because {argument c}

* Bad, because {argument d}

* …


### No historic data is captured

{example | description | pointer to more information | …}

* Good, because {argument a}

* Good, because {argument b}

* Neutral, because {argument c}

* Bad, because {argument d}

* …


## More Information

{You might want to provide additional evidence/confidence for the decision outcome here and/or document the team agreement on the decision and/or define when/how this decision the decision should be realized and if/when it should be re-visited. Links to other decisions and resources might appear here as well.}

### ~~Requirements~~

* ~~The structure must beEnd of the insertion able represent a tree, where every node has metadata, Begin of the insertiontoo.~~End of the insertion Begin of the deletion too.End of the deletion

* Begin of the insertion~~Historical data~~End of the insertion Begin of the deletion Historical dataEnd of the deletion

* Begin of the insertion~~IfEnd of the insertion Begin of the deletion IfEnd of the deletion the hierarchy is changed, it will result in conflict with already assigned Begin of the insertionvalues~~End of the insertion Begin of the deletion valuesEnd of the deletion

* Begin of the insertion~~WeEnd of the insertion Begin of the deletion WeEnd of the deletion must be able to preserve historical value assignments, which also need access to the historical Begin of the insertionhierarchy~~End of the insertion Begin of the deletion hierarchyEnd of the deletion

* Begin of the insertion~~WeEnd of the insertion Begin of the deletion WeEnd of the deletion must be able to update conflicting value assignments -> Important: auditability Begin of the insertion(journals)~~End of the insertion Begin of the deletion (journals)End of the deletion

* Begin of the insertion~~FilteringEnd of the insertion Begin of the deletion FilteringEnd of the deletion must be able to find values based on historical hierarchies (filter query language Begin of the insertionneeded?)~~End of the insertion Begin of the deletion needed?)End of the deletion


### Begin of the insertion~~IMPORTANT~~End of the insertion Begin of the deletion IMPORTANTEnd of the deletion

* Begin of the insertion~~weEnd of the insertion Begin of the deletion weEnd of the deletion need to document all decisions, as there will be some heavy Begin of the insertionlifters~~End of the insertion Begin of the deletion liftersEnd of the deletion