[Hawkular-dev] Serialization format for inventory relations

[Jiri Kremser]

hi,

| Link: rel="child", href="http://bla/bla"
| 
| 
| Are you talking here about exposing the relationships only?
| If you don't plan to include the resources in the result,
| would be a list of links not enough?

The source and the target of the relationship are also present in the data. This is how it works:

send GET to /hawkular/inventory/.../relationships and you'll get all the relationships of the ...
so for instance /hawkular/inventory/acme/prod/resources/host42/relationships will return all the relationships (and the basic info of the other side of this relationship, i.e. where host42 functions as a target and those where host42 acts as a source)

I guess "Link: rel="child", href="http://bla/bla" is a good way how to address one resource from another one, but we need to expose the information about the relationship itself, it can have properties.

 
| > Here is an example of 1 relation/edge:
| >
| > {
| > "@context": {
| >  "inv": "http://hawkular.org/inventory/0.0.1",
| >  "baseUrl": "http://127.0.0.1:8080/hawkular/inventory/"
| > },
| > "@id": "baseUrl:relationships/1337",
| > "inv:shortId": "2",
| > "@type": "inv:Relationship",
| > "inv:source": {
| >  "@id": "baseUrl:tenants/acme",
| >  "@type": "inv:Tenant",
| >  "inv:shortId": "acme"
| > },
| > "inv:label": "contains",
| > "inv:target": {
| >  "@id": "baseUrl:acme/resourceTypes/URL",
| >  "@type": "inv:ResourceType",
| >  "inv:shortId": "URL"
| > },
| 
| This doesn't really show me its strengths at the moment and looks
| bloated. But perhaps the strength is that the relationship target
| has its type supplied?

in fact it could look like this and it'll be still json-ld:

{
  "@context": "http://hawkular.org/inventory/0.0.1/relationship.jsonld",
  "@id": "baseUrl:relationships/1337",
  "shortId": "1337",
  "source": "baseUrl:tenants/acme",
  "label": "contains",
  "target": "baseUrl:acme/resourceTypes/URL"
}

It's up to us how much information we expose, almost everything can be remotely referenced. But I think the entity type is a good thing to have in the data.


| Do we expect to use some existing clients to browse and visualize
| our inventory using JSON-LD?

it's one of the standards for storing the <subject,predicate,object> triples and it can be converted [1] to RDF, so yes, there are tools out there for visualizing the structure


| The other question is if the query is 'give me all related entities to
| this entity'
| as you describe above, should we really "only" return the links? 

definitely, this can be tweak once we find out what we want from the UI perspective. There can be a path/query parameter that will embed the entities (with all the fields including the property hashmap) into the response instead of the link.

| Or how
| will we treat the fetching of the target entities? Can they optionally
| be embedded in the answer?

yes, json-ld supports embedding [2]. Currently, the source and target contain the name (shortId), type and the URL if we need to fetch more/less information.

[1]: http://www.w3.org/TR/json-ld-api/#deserialize-json-ld-to-rdf-algorithm
[2]: https://www.youtube.com/watch?v=UmvWk_TQ30A&t=3m05s