Frames

This is a framework for frames, in Logtalk.

What is a frame?

Conceptually a frame is a data structure that has a subject, which is its identity, and slots. These slots also have unique names and can contain many values for each slot. They also support inheritence of slots.

Most often frames are used with daemons, which are additional rules that can be queried at various points. For example, when reading a value from a slot a "calculate" daemon may be triggered for a particular slot that will calculate the value instead of looking it up.

Frames are useful in that they combine data with rules for knowledge representation.

Expected data format

This framework expects the data to be represented in SPO format, meaning:

{ subject: {predicate: [objects]} }

Where there can be many of each subject, predicate, or objects, and objects is an ordered list (set). See test_db.json for an example. JSON is not required, but it does work well.

In terms of the language used, two calculation categories are provided. slimowl_inheritance uses type to denote the slot describing what type of thing the subject is: a 'Class', or in the case of an instance, a 'NamedIndividual' and what class it is instantiating. subClassOf is used for the slot that is used for inheritence. This is to stay close to the language of the semantic web. classic_inheritance uses the classic terms isa and ako for "is a" and "a kind of", where isa denotes instantiation and ako denotes subsumption. You can re-use these as you wish, or create your own for your use-case and set it as a daemon.

Adding daemons

Daemons are added as facets to frames. Simply implement the calculate_protocol as an object. The test-case calculate_attrs is a good example. It works like so:

:- object(height_calculator,
	implements(calculator_protocol)).

	calculate(Frames, Subject, height(inches), Height) :-
		frames::get_slot(Frames, Subject, height-Height).

	calculate(Frames, Subject, height(cm), Height) :-
		frames::get_slot(Frames, Subject, height-Inches),
		Height is Inches*2.54

:- end_object.

This is then available as a facet, enabling these queries:

   frames::get_frame(TestDBFrames, 'Carrot', [height(inches)-Inches, height(cm)-CM]).

Inches = 12,
CM = 30.48 .

To add many kinds of calculators, such as one for units as above and perhaps another for translation (which could be querying another frame collection in predicate-language-value order), you might find it useful to create a calculator interface into which you import your different kinds of calculators. In this way you can compose sophisticated knowledge bases.

For other daemons, check daemon_protocols to find supported predicates, they work in the same way (with the plugin-architecture).

Frame queries

By CRUD:

Create

• new/1 : new(FrameCollection) is to get a new, empty collection of frames
• add_frame/4 : add_frame(OldFrames, Subject, [KeyValuePairs], NewFrames), adds the values at a key to subject. KeyValuePairs can be Key-NewValue or Key-OldValue to NewValue so that the OldValue can be unified or checked. Handles both single values and lists, as well as adding new subjects.

Read

• get_frame/3 : get_frame(FrameCollection, Subject, [Key-Value|Pairs]), uses reasoning, query many slots of a frame.

• get_slot/3 : get_slot(FrameCollection, Subject, Key-Value), uses reasoning, only a single slot for a frame.

• get_data/3 : get_data(FrameCollection, Subject, Key-Value), no reasoning, just does a lookup in the frame collection.

Update

• update_frame/4 : update_frame(OldFrames, Subject, [KeyValuePairs], NewFrames), updates the values at a key in subject. KeyValuePairs can be Key-NewValue or Key-OldValue to NewValue so that the OldValue can be unified or checked. Handles both single values and lists.

Delete

• delete_frame/3 : delete_frame(OldFrames, Subject, NewFrames), removes the whole frame from the collection, providing the new collection. Only deletes the frame, it doesn't delete references to the frame. WIP: No daemon support yet.
• delete_frame/4: delete_frame(OldFrames, Subject, [KeyValuePairs], NewFrames), deletes the Key-Value pairs from the frame. If the values at the key are a list, then only the element is deleted. If the value at the key isn't a list or if it's the last one, then the whole key is deleted.

See Also

• Frames Persistency, a plugin that when loaded will manage basic, to disk persistency for use with this frames framework.