Grakn, create entity composed by entity?

Question

I'm very new on GRAKN.AI and I'm wondering if in a GRAKN's graph I can create an "entity" composed by an "enitity". I know I can do the following code:

table sub entity
   has book;

book sub resources datatype string;

But can I relate the "book" as an entity to the "table" ??

I need to have "book" as a complex concept and not as a simple resource.

Thanks,

Davide.

Answer 1

An alternative solution is to go through a relationship which allows you to define things more explicitly. For example,

To define a relationship you start by defining roles which provide context for how things relate to each other. For example:

insert
    thing-on-top-of-table sub role;
    table-with-thing-on-top sub role;

You then say how these roles link to the relationship and to the entities:

insert    
    sits-on sub relation 
        relates thing-on-top-of-table
        relates table-with-thing-on-top;
    table plays table-with-thing-on-top;
    book plays thing-on-top-of-table;

The above is pretty much the schema of your simple knowledge base.

Now we can add some data. Let's say some book is on top of some table:

insert 
    $book isa book;
    $table isa table;
    (thing-on-top-of-table: $book, table-with-thing-on-top: $table) isa sits-on

Naturally you can expand things from here. For example you can give your book a title via a resource.

Side Note: Resources Vs Entities

The basic rule of thumb for relating something as a resource or as another entity depends on how much information you want to express in the model as well as if something can be defined by a data literal (e.g. String, Int, Long, etc . . . ).

For example a book is an entity because it is made up of multiple resources which help identify the book. I.e. the title, isbn, etc. . . those resources on the other hand are simple data values. A title is nothing but a string so there is no reason to make the title an entity, that should be fine as just a resource.