Edit on Github

Update Instances of Concepts

In a Grakn knowledge graph, each instance is a “fact”. Relations and entities are extensible and reducible, by adding or removing role players to them over time. Each attribute value can be owned and the ownership can be removed or added: updating an attribute value directly therefore means changing the attribute value for ALL owners of this attribute value! Achieving this requires deleting the attribute value and connecting previous owners to a different value instance. Updating the attribute value that is owned by a concept means changing the connection to the value, rather than the value itself. We can achieve this in a single query using an Update query, which consists of a match, a delete, and an insert.

To try the following examples with one of the Grakn clients, follow these Clients Guide.

Update attribute owned by a concept

Usually, we want to change the value of an attribute that is associated to another instance. To do so, we first need to delete the association that the instance has with the attribute of interest and then insert the new instance of the attribute. We can do this in a single update query as follows:

[tab:Graql] ```graql ## disconnecting from the old attribute value match $org isa organisation, has name "Medicely", has registration-number $rn; delete $org has $rn; insert $org has registration-number "81726354"; ``` [tab:end] [tab:Java] ```java GraqlUpdate update_query = Graql.match( var("org").isa("organisation").has("name", "Medicely").has("registration-number", var("rn")) ).delete( var("org").has(var("rn")) ).insert( var("org").has("registration-number", "81726354") ); ``` [tab:end]

This query first deletes the association that the organisation with id V17391 has with the instance of the registration-number attribute type and then continues to insert the new instance of the registration-number to be owned by the same instance of organisation.

Update all instances of a given attribute

There may also be cases where we need to update the value of all instances of an attribute type. This amounts to rewriting the value of an attribute fact. To do so, we can again make use of an update query.

[tab:Graql] ```graql match $m isa media, has caption $c; $c contains "inappropriate word"; delete $c isa caption; insert $m has caption "deleted"; ``` [tab:end] [tab:Java] ```java GraqlUpdate update_query = Graql.match( var("m").isa("media").has("caption", var("c")), var("c").contains("inappropriate word") ).delete( var("c").isa("caption") ).insert( var("m").has("caption", "deleted") ); ``` [tab:end]

This query first looks for any instance of type media that owns the caption attribute containing an "inappropriate word", then for each media-attribute pair it finds, deletes the caption and inserts a caption reading deleted in its place.

Modifying a relation’s role player

To replace a role player, we combine the steps for extending the relation, with steps for deleting a role player:

[tab:Graql] ```graql match $org isa organisation, has name "Pharos"; $new-org isa organisation, has name "Medicely"; $emp (employer: $org, employee: $p) isa employment; delete $emp (employer: $org); insert $emp (employer: $new-org); ``` [tab:end] [tab:Java] ```java GraqlUpdate update_query = Graql.match( var("org").isa("organisation").has("name", "Pharos"), var("new-org").isa("organisation").has("name", "Medicely"), var("emp").rel("employer", "org").rel("employee", "p").isa("employment") ).delete( var("emp").rel("employer", "org") ).insert( var("emp").rel("employer", "new-org") ); ``` [tab:end]

After these queries, all employments by the organisation named Pharos were replaced employments by the organisation named Medicely.

Clients Guide

[Note] **For those developing with Client [Java](../client-api/java)**: Executing an `update` query, is as simple as calling the [`query().update()`](../client-api/java) method on a transaction and passing the query object to it.
[Note] **For those developing with Client [Node.js](../client-api/nodejs)**: Executing an `update` query, is as simple as passing the Graql(string) query to the `query().update()` function available on the [`transaction`](../client-api/nodejs#transaction) object.
[Note] **For those developing with Client [Python](../client-api/python)**: Executing an `update` query, is as simple as passing the Graql(string) query to the `query().update()` method available on the [`transaction`](../client-api/python#transaction) object.

Summary

Updating data in Graql is usually involves an update query, which takes the form of match-delete-insert. You can use these queries to add and remove role players from relations, or add and remove ownerships of attributes. Attribute values themselves can be treated as immutable, and changing their values amounts to deleting the value and moving all the ownerships of the old value to some new value.

Next, we learn how to aggregate values over a set of data in a Grakn knowledge graph.