- Delete Instances of a Type
- Delete Attribute Ownerships
- Delete Role Players from Relations
- Clients Guide
Delete Instances of a Type
To delete an instance of a type from the knowledge graph, we use a match clause followed by the
delete keyword and statements indicating data to delete.
To try the following examples with one of the Grakn clients, follows these Clients Guide.
Match-Delete queries are NOT lazy: the
match will be fully evaluated and answers recorded, and each answer will in turn have
the operations specified in the
delete clause applied. This avoids modifying the graph while traversing it.
This deletes a particular instance of the
person type with the email
email@example.com. We must write the
isa clause to tell
the parser to remove the instance of data represented by the variable
$p. If we don’t know the type, we can usually use
the supertype of all data instances.
Deleting an instance of a relation type follows exactly the same style:
This deletes all instances of the
employment type where the
employer is an
Attributes are normally owned by other concepts (ie.
$x has attribute $a). This means we can both delete an attribute
ownership, as in the next section, or delete the instance itself following the above style of using
isa in the delete clause.
Delete Attribute Ownerships
We can remove the ownership of an attribute by another concept in the same way it is inserted or queried: using the
Note that attributes with the same value and type are shared among their owners. For this reason, usually, an attribute is not deleted directly.
This looks for a
travel that owns the attribute
start-date with the value of
2013-12-22 in the
We then disassociate the
$t from the attribute
$st with the
delete $t has $st clause.
This will not delete the entire instance of type
start-date and value
2013-12-22 - it remains associated with any other instance that may own it.
If we had instead written the query as
match $t isa travel, has start-date $st; $st == 2013-12-22"; delete $st isa start-date;,
we would have deleted the instance of
start-date with value
2013-12-22 and its association with all other concept types that previously owned it.
Note also that you must not specify a type for the attribute when deleting, as this creates a derived
isa constraint on the attribute. You must use
delete $t has $st, not
delete $t has start-date $st.
Delete Role Players from Relations
In Grakn, existing relations can be extended with new role players, or shrunk by removing role players.
If an employer merged with another, we may have to reassign all existing
employment relations to the new company.
To remove the old employer from the employment relation, we mirror the
delete syntax with what the
for role players looks like.
This Graql query will find all employments where the employer is an organisation with the name
Pharos. It will then
remove the organisation from the employment relation. It is required to provide the role that the role player is playing
delete statement. If the role is unknown, it is possible to use the generic
delete block, though being as specific as possible is recommended.
delete query preceded by a
match clause is used to delete one or more facts from the knowledge graph.
We can delete instances by using
$var isa [your type]: an
isa will always indicate removal of an instance and all its edges.
Additionally, we can remove just attribute ownerships using the
has statement in the
delete clause. Removing
a role player from a relation can similarly be achieved by using role player syntax:
delete $r (some_role: $player); without
Next, we learn how to update data in a Grakn knowledge graph.