如何在Grakn知识图谱中表示知识库随时间的变化？

Great question! Tracking how facts evolve over time in Grakn (now rebranded as TypeDB) is a common use case, and there are two straightforward, idiomatic approaches to handle your scenario. Let's walk through them with your example:

1. Model Time Intervals Directly in Your Schema #

The most explicit way is to add temporal attributes to the relationships that change over time. For your teacher-class association:

Step 1: Define the Schema #

First, set up your entities, relations, and attributes to support time tracking:

define
person sub entity, has name;
class sub entity, has student-count;
teaching sub relation,
  relates teacher,
  relates taught-class,
  has start-date,
  has end-date;
name sub attribute, value string;
student-count sub attribute, value long;
start-date sub attribute, value datetime;
end-date sub attribute, value datetime;

Step 2: Insert Version 1 (Jan 2016) #

Record Rachel's tenure with a start date and an end date marking when she was replaced:

insert
$rachel isa person, has name "Rachel";
$math-class isa class, has student-count 10;
$rachel-teaches isa teaching,
  relates teacher $rachel,
  relates taught-class $math-class,
  has start-date 2016-01-01T00:00:00,
  has end-date 2016-03-01T00:00:00;

Step 3: Insert Version 2 (Mar 2016) #

Add Alice's teaching relationship with her start date (leave end-date unset if she's currently the active teacher):

insert
$alice isa person, has name "Alice";
$alice-teaches isa teaching,
  relates teacher $alice,
  relates taught-class $math-class,
  has start-date 2016-03-01T00:00:00;

Querying by Time #

To get the teacher for the class in Feb 2016:

match
$class isa class, has student-count 10;
$teaching isa teaching,
  relates taught-class $class,
  has start-date $start,
  has end-date $end;
$teacher isa person, has name $name, relates teacher $teaching;
$start <= 2016-02-01T00:00:00;
$end >= 2016-02-01T00:00:00;
get $name;

2. Leverage Grakn's Built-in History Tracking #

Grakn automatically logs all changes to your data, so you can query the state of the graph at a specific point in time without explicitly adding time attributes.

Step 1: Insert Initial State #

First, insert the Jan 2016 state without explicit time attributes:

insert
$rachel isa person, has name "Rachel";
$math-class isa class, has student-count 10;
(teacher: $rachel, taught-class: $math-class) isa teaching;

Step 2: Apply the Change (Mar 2016) #

When you need to update the teacher, delete the old relationship and insert the new one:

match
$rachel isa person, has name "Rachel";
$math-class isa class, has student-count 10;
$old-teaching (teacher: $rachel, taught-class: $math-class) isa teaching;
delete $old-teaching;

insert
$alice isa person, has name "Alice";
(teacher: $alice, taught-class: $math-class) isa teaching;

Query Historical State #

To retrieve the teacher as of Feb 2016, use Grakn's temporal query capabilities (note: this requires enabling history in your database configuration):

match @as-of 2016-02-01T00:00:00
$class isa class, has student-count 10;
$teacher isa person, has name $name;
(teacher: $teacher, taught-class: $class) isa teaching;
get $name;

Which Approach Should You Use? #

• Use time intervals if you need to explicitly model tenure periods, or if you want to query overlapping time ranges easily.
• Use built-in history if you want a simpler schema and just need to audit past states without manual time tracking.

内容的提问来源于stack exchange，提问作者Gregorio Momm