Constraints for edges

[lvca]

Recently asked on Discord, but discussed in many other topics and issues, we'd need a way to create constraints for edges so they can be attached only to specific vertex types.

The most natural way to achieve this is to mimic what OrientDB does: create constraints on out and in properties. While in OrientDB out and in are real properties in the document, with ArcadeDB are managed in binary form (much faster), but then exposed to the users as respectively @out and @in metadata.

To provide constraints on edge we could simply allow the following syntax alter property Friend.@out linkedtype Account;alter property Friend.@in linkedtype Account (in OrientDB was LINKEDCLASS). This would mean Friend edge type can only connect Account to another Account.

[lvca]

This would also allow displaying the graph model in Studio (#739)

[gramian]

I ilke the idea and the syntax, but how about:

• using only instead of linkedtype?
• allowing arrays here to permit multiple linakable types?

[malakeel]

good point. How about inheritance ? Can we allow overriding ? For example:

User --> HasAccount -> Account
SystemUser extends User
Account extends SystemAccount

Do we implicitly allow SystemAccount to link to Account ?

[lvca]

Yes, the inheritance will be used, so if you link the base type, all the subtypes will be allowed.

@gramian what about of type? Examples (SQL KEYWORD IN UPPER CASE):

ALTER PROPERTY Friend.@out OF TYPE Account;
CREATE PROPERTY User.data embedded OF TYPE UserData;
CREATE PROPERTY User.keywords list OF TYPE string;

So we can use the same for limiting embedded properties, like EMBEDDED and LIST.

WDYT?

[gramian]

I can see the appeal of this, but to me the typing of properties feel like constraints, so I thought wrt syntax of CREATE PROPERTY like:

CREATE PROPERTY User.keywords LIST (type string)

hence only, but oftype would work (for me) too. And the SQL grammar wouldn't have to be touched, right?

[lvca]

Moving this discussion to an issue: #1174