How to run PowerLoom Interactively in Java Artificial Intelligence Programming

Running PowerLoom:

We will experiment with PowerLoom concepts, relations, and rules in this section in an interactive command shell. I will introduce more examples of PowerLoom functionality for asserting instances of concepts, performing queries, loading PowerLoom source files, defining relations, using separate modules, and asking Power-Loom to explain the inference process that is used for query processing.

You can run PowerLoom using the command line interface by changing directory to the lib subdirectory from the ZIP file for this book and trying:

java -cp powerloom.jar:stella.jar \\

edu.isi.powerloom.PowerLoom

This starts the PowerLoom standalone system and prints a prompt that includes the name of the current module. The default module name is “PL-USER”. In the first example, when I enter the person concept at the interactive prompt then PowerLoom prints the result of the expression that just entered.

PL-USER |= (defconcept person)

|c|PERSON

PL-USER |= (defconcept parent (?p person))

|c|PARENT

PL-USER |= (defrelation parent-of

((?p1 parent) (?p2 person)))

|r|PARENT-OF

PL-USER |= (assert (person Ken))

|P|(PERSON KEN)

PL-USER |= (assert (person Mark))

|P|(PERSON MARK)

PL-USER |= (assert (parent-of Ken Mark))

|P|(PARENT-OF KEN MARK)

Now that we have entered two concepts, a test relation, and asserted a few facts, we

can look at an example of PowerLoom’s query language:

PL-USER |= (retrieve all ?p (person ?p))

There are 2 solutions:

#1: ?P=MARK

#2: ?P=KEN

PL-USER |= (retrieve all ?p (parent ?p))

There is 1 solution:

#1: ?P=KEN

PL-USER |=

The obvious point to note from this example is that we never specified that Ken was a parent; rather, PowerLoom deduced this from the parent-of relation.

PowerLoom’s command line system prompts you with the string “PL-USER —=“ and you can type any definition or query. Like Lisp, PowerLoom uses a prefix notation and expressions are contained in parenthesis. PowerLoom supports a module system for partitioning concepts, relations, functions, and rules into different sets and as previously mentioned “PL-USER” is the default module. PowerLoom modules can form a hierarchy, inheriting concepts, relations, and rules from parent modules.

The subdirectory test data contains the demo file business.plm written by Robert MacGregor that is supplied with the full PowerLoom distribution. You can load his complete example using:

PL-USER |= (load "../test_data/business.plm")

This is a good example because it demonstrates most of the available functionality of PowerLoom in a short 200 lines. When you are done reading this chapter, please take a few minutes to read through this example file since I do not list it here. There are a few things to notice in this example. Here we see a rule used to make the relation “contains” transitive:

(defrelation contains (

      (?l1 geographic-location)

           (?l2 geographic-location)))

(defrule transitive-contains (=> (and (contains ?l1 ?l2)

         (contains ?l2 ?l3))

          (contains ?l1 ?l3)))

The operator => means that if the first clause is true then so is the second. In English, this rule could be stated “if an instance i1 contains i2 and if instance i2 contains i3 then we can infer that i1 also contains i3.” To see how this rule works in practice, we can switch to the example module “BUSINESS” and find all locations contained inside another location:

PL-USER |= (in-module "BUSINESS")

BUSINESS |= (retrieve all

(?location1 ?location2)

(contains ?location1 ?location2))

There are 15 solutions:

#1: ?LOCATION1=SOUTHERN-US, ?LOCATION2=TEXAS

#2: ?LOCATION1=TEXAS, ?LOCATION2=AUSTIN

#3: ?LOCATION1=TEXAS, ?LOCATION2=DALLAS

#4: ?LOCATION1=UNITED-STATES, ?LOCATION2=SOUTHERN-US

#5: ?LOCATION1=GEORGIA, ?LOCATION2=ATLANTA

#6: ?LOCATION1=EASTERN-US, ?LOCATION2=GEORGIA

#7: ?LOCATION1=UNITED-STATES, ?LOCATION2=EASTERN-US

#8: ?LOCATION1=SOUTHERN-US, ?LOCATION2=DALLAS

#9: ?LOCATION1=SOUTHERN-US, ?LOCATION2=AUSTIN

#10: ?LOCATION1=UNITED-STATES, ?LOCATION2=DALLAS

#11: ?LOCATION1=UNITED-STATES, ?LOCATION2=TEXAS

#12: ?LOCATION1=UNITED-STATES, ?LOCATION2=AUSTIN

#13: ?LOCATION1=EASTERN-US, ?LOCATION2=ATLANTA

#14: ?LOCATION1=UNITED-STATES, ?LOCATION2=GEORGIA

#15: ?LOCATION1=UNITED-STATES, ?LOCATION2=ATLANTA

BUSINESS |=

Here we have fifteen solutions even though there are only seven “contains” relations asserted in the business.plm file – the other eight solutions were inferred. In addition to the “retrieve” function that finds solutions matching a query you can also use the “ask” function to determine if a specified relation is true; for example:

BUSINESS |= (ask (contains UNITED-STATES DALLAS))

TRUE

BUSINESS |=

For complex queries you can use the “why” function to see how PowerLoom solved the last query:

BUSINESS |= (ask (contains southern-us dallas))

TRUE

BUSINESS |= (why)

1 (CONTAINS ?location1 ?location2)

follows by Modus Ponens

with substitution {?l1/SOUTHERN-US, ?l3/DALLAS,

?l2/TEXAS}

since 1.1 ! (FORALL (?l1 ?l3)

(<= (CONTAINS ?l1 ?l3)

(EXISTS (?l2)

(AND (CONTAINS ?l1 ?l2)

(CONTAINS ?l2 ?l3)))))

and 1.2 ! (CONTAINS SOUTHERN-US TEXAS)

and 1.3 ! (CONTAINS TEXAS DALLAS)

BUSINESS |=

By default the explanation facility is turned off because it causes PowerLoom to run more slowly; it was turned on in the file business.plm using the statement: (set-feature justifications)