Knowledge Bases
Knowledge is organized into named repositories called knowledge bases. A knowledge base is like a directory for files on disk, except that knowledge bases may not be nested. Therefore, the entities within a knowledge base always have a two-level name: knowledge_base_name.knowledge_entity_name.
Here are some examples of facts you might see in a web server application:
header.cookie('session=123456789;remember=the_alamo')
cookie.session(123456789)
cookie.remember(the_alamo)
header.accept_encoding(gzip)
header.accept_encoding(deflate)
request.path('/my/site.html')
request.path_segment(0, my)
request.path_segment(1, 'site.html')
request.path_segment(-2, my)
request.path_segment(-1, 'site.html')
Note that three different knowledge bases (all fact bases) are shown here named header, cookie, and request; each with multiple facts.
The second part of the two-part name is the name of the knowledge entity. You can think of knowledge entities as statement types or topics. So:
request: is the name of the knowledge base. request.path_segment: is the name of the knowledge entity, or statement topic. request.path_segment(-1, 'site.html'): is a specific statement about the topic of request.path_segments.
What do Knowledge Bases Do?
Ultimately Pyke is interested in proving statements, or answering the question "Is statement X true"? There are several different types of knowledge bases. Each type of knowledge base represents a different way of doing this:
- Those that contain simple lists of statements of fact (as you see in the
example above) are called fact bases.
- These determine whether a statement is true by simply checking to see if that statement is in their list of known facts.
- Those that contain if-then rules are called rule bases.
- These determine whether a statement is true by running their if-then rules to try to construct a proof for that statement.
- Rule bases may include both forward-chaining and backward-chaining rules.
- It is also possible to create other kinds of knowledge bases that determine
the truth of statements in other ways. Pyke provides two of these:
- The question base which just poses the statement to an end user as a question.
- The special knowledge base which has several special one-off knowledge
entities to do different things like run a command on the underlying
system and examine its output and/or exit status.
- There is only has one instance of this knowledge base -- called special.
Note
All knowledge bases share the same name space. So no two of them, regardless of their type, may have the same name.