Where to store type metadata?

TypeDB
1

Is there an elegant way to store type metadata?

Examples:

  • We want entities of type T1 to be displayed at the diagram as a circle, and type T2 – as a square
  • We have to attach to the string attribute a list of allowed values (not as a db constraint but for use in the UI)
  • We want to mark an attribute as read-only for the UI

We can store it outside of TypeDb of course, but it would be more consistent to use some internal mechanics to do this.

2

I can think of two possible approaches, each with their pros and cons:

1. Metadata as schema

define
diagram-shape-circle sub attribute, value long;
diagram-shape-square sub attribute, value long;
t1 sub entity, owns diagram-shape-circle;
t2 sub entity, owns diagram-shape-square;

readonly sub attribute, value boolean;
t3 sub attribute, value string;
t4 sub attribute, value string, owns readonly;

Easy to query using schema queries, not very extensible though and may require regular schema updates which can interrupt regular usage of the DB.

2. Metadata as data

There are a few options here - the solution proposed here may not be the most elegant model, but it is one option:

define
type-metadata sub entity, abstract, owns type-label;
type-metadata-diagram-shape sub type-metadata, owns diagram-shape;
type-metadata-is-readonly sub type-metadata, owns is-readonly;

type-label sub attribute, value string;
diagram-shape sub attribute, value string;
is-readonly sub attribute, value boolean;

t1 sub attribute, value long;
t2 sub attribute, value string;
...

insert
$t1 "t1" isa type-label;
$t2 "t2" isa type-label;
$diagram_shape_circle "circle" isa diagram-shape;
$diagram_shape_square "square" isa diagram-shape;
$readonly_true true isa is-readonly;
$tm1 isa type-metadata, owns $t1, owns $diagram_shape_circle, owns $readonly_true;
$tm2 isa type-metadata, owns $t2, owns $diagram_shape_square;

Queries are slightly longer, but can be significantly more expressive. We are able to define a type for every possible “metadata ownership”, and create these metadata ownerships (subtypes of type-metadata) on the fly by inserting them as data.

It might even be more elegant to have the type-label own the metadata directly - however, be aware that attributes owning other attributes is a rarely-used feature of TypeDB and could be deprecated in future versions :slight_smile:

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