Course 7. First rule-based app Java and Jess

Transcription

1 Course 7 First rule-based app Java and Jess

2 Tax form advisor asks the user a series of questions based on the answers, tells the user which form is needed populate the application with data a command-line interface concentrate on developing the rules themselves so the entire program will be written in Jess

3 Collecting the knowledge information will include: Requirements Looking at the problem the system needs to solve is the first step - may continue Principles You need to learn the organizing principles of the field. Resources Frontiers the though bits, ambiguities, and limits

4 Collecting the knowledge (cont.) iterative process: first talk to the customers: their needs + resources Requirements engineering Technical sources of information Study general resources learn fundamentals of the domain First knowledge extraction Q1 A1 Q2 A2...

5 Collecting the knowledge (cont.) find cooperative experts interview > more information - organize Rules

6 Collecting the knowledge (cont.) (defrule use-ez-form ; If filing status is "single", and... (filing-status single) ) ; user made less than $50000 (income?i&:(<?i 50000)) => ; recommend the user file Form 1040EZ (recommend Form1040EZ)

7 Collecting the knowledge (cont.) Verify so far: Customers Users Domain experts End of phase: organize data deftemplates Organize rules defmodules write some infrastructure: functions for input and output

8 Designing the application possible candidates for deftemplate types: form A specific tax form user The operator of the system deduction A way of reducing your taxable income credit A way of reducing your tax burden dependent A person the user cares for General organization of the application suggests: question A question the system might ask the user answer An answer given by the user recommendation A note that the system will recommend a specific form decide what form they will take ordered or unordered facts what slots should they have (unordered)

9 Designing the application (cont.) Forms (deftemplate form (slot name)(slot description)) Questions and answers Value, yes/no (deftemplate question (slot text) (slot type) (slot ident)) (deftemplate answer (slot ident) (slot text)) recommendation (deftemplate recommendation (slot form) (slot explanation)) Complete?

10 Designing the application (cont.) sketch out a structure for how the rules will be organized O The Tax Forms Advisor: Modules: 1. Initialize the application Startup 2. Conduct an interview - determine tax situation Interview 3. Figure out what tax forms to recommend Recommend 4. Present list of forms to the user, removing Report any duplicate recommendations

11 Designing the application (cont.) Module groups facts + rules!!! Different modules cannot share the same deftemplate => move to MAIN Templates question and answer used by interview and recommend modules, all deftemplates defined in MAIN

12 Designing the application (cont.) Print question + read answer (deffunction ask-user (?question) ) "Ask a question, and return the answer" (printout t?question " ") (return (read))

13 Designing the application (cont.) Check answer (deffunction is-of-type (?answer?type) "Check that the answer has the right form" (if (eq?type yes-no) then (return (or (eq?answer yes) (eq?answer no))) else (if (eq?type number) then (return (numberp?answer))) else (return (> (str-length?answer) 0))))

14 Writing the application (defmodule startup) (defmodule interview) (defmodule recommend) (defmodule report) (deffunction run-system () (reset) (focus startup interview recommend report) (run) )

15 Java & Jess

16 Using Java from Jess functions - create and manipulate Java objects directly from Jess work same as Java code, including defining new classes. (bind?ht (new java.util.hashmap)) <Java-Object:java.util.HashMap> (call?ht put "key1" "element1") (?ht put "key2" "element2") Jess can access member variables of Java objects (bind?pt set (new and java.awt.point)) get (set-member?pt x 37) set-member and get-member work with instance variables;

17 Transferring values between Jess and Java code class jess.rete: public Value store(string name, Value val); public Value store(string name, Object val); public Value fetch(string name); public void clearstorage(); Functions in Jess: (store <name> <value>) (fetch <name>) (clear-storage) import jess.*; public class ExFetch {public static void main(string[] unused) throws JessException { Rete r = new Rete(); r.store("dimension", new java.awt.dimension(10, 10)); r.eval("(bind?list (list dimension (fetch DIMENSION)))"); r.eval("(printout t?list)"); } } C:> java ExFetch (dimension <Java-Object:java.awt.Dimension>)

18 Implementing Java interfaces with Jess function implement : name of an interface name of a deffunction, returns an object that implements that interface by calling that function. When any method of that interface is invoked, the deffunction will be called first argument will be the name of the interface function, then all the arguments of the interface function (import java.util.comparator) (deffunction compare(?name?s1?s2) (return ((?s1 touppercase) compareto (?s2 touppercase)))) (bind?c (implement Comparator using compare))

19 Using Jess in Java 2 main ways in which Java code can be used with Jess: Java can be used to extend Jess Jess library can be used from Java.

20 jess.rete class the rule engine itself each jess.rete object has its own working memory, agenda, rules, etc. create one or more jess.rete objects and manipulate them: load in the catalog data, load in the rules

21 instance of jess.rete - an instance of Jess Rete class exports methods for: adding, finding, and removing facts, rules, functions, and other constructs Rete class - facade for Jess library

22 create a jess.rete object. - default constructor (one that accepts no arguments): import jess.*;... Rete engine = new Rete();

23 executecommand method accepts a String argument and returns a jess.value Interpreted as an expression Return value = result of evaluation Only a single call to executecommand can be simultaneously executing on a given instance of jess.rete import jess.*;... Example: add a fact to Jess s working memory and get access to the jess.fact object Rete engine = new Rete(); Value v = engine.executecommand("(assert (color red))"); Fact f = v.factvalue(engine.getglobalcontext());

24 store, fetch work in both directions Some Jess functions are wrappers for methods in the jess.rete class: run(), run(int), reset(), clear(), assertfact(fact), retract(fact), retract(int), and halt() jess.rete.eval(java.lang.string) - execute, from Java, any Jess function call or construct definition that can be represented as a parseable String Rete r = new Rete(); r.eval("(deffunction square(?n)(return(*?n?n)))"); Value v = r.eval("(square 3)");

25 Working with facts construct jess.fact objects directly Rete method Jess equivalent adddeftemplate(deftemplate) (deftemplate) assertfact(fact) (assert fact) finddeftemplate(string) - findfactbyfact(fact) - findfactbyid(int) (fact-id number) retract(fact) (retract fact-id)

26 jess.fact class - subclass of ValueVector All the entries in the ValueVector correspond to slots of the Fact; data for the first slot is the item at index 0. The head or name of the fact is stored in a separate variable jess.fact - associated jess.deftemplate object (desc.) All Facts with a given head should share the same Deftemplate.

27 Adding Commands to Jess add user-defined functions to Jess import jess.*; public class ExAddUF { public add static new void functions main(string[] to argv) the throws Jess language: JessException { write // a Add class the that 'my-upcase' implements command the to Jess Rete jess.userfunction r = new Rete(); interface r.adduserfunction(new ExMyUpcase()); create // This a single will print instance "FOO of this class install System.out.println(r.eval("(my-upcase it into a jess.rete object foo)")); using } Rete.addUserfunction() } C:\> java ExAddUF Jess> (load-function ExMyUpcase) "FOO" Jess> (my-upcase foo) "FOO"

28 Create GUI in Jess Jess - incorporated as a library into graphical applications written in Java. write graphical applications in the Jess language: Implement the appropriate interface (import java.awt.*) (import java.awt.event.*) (defglobal?*f* = (new Frame "Button Demo")) ;; Create the widgets

29 Jess and XML Representing rules as XML Interoperability Editability Searchability RuleML Standard, but under development RHS not well supported JessML XML rule format can be transformed into Jess rules using an XSLT script

30 Example <?xml version="1.0"?> <!DOCTYPE rulebase SYSTEM "jess.dtd"> <rulebase> <rule name="animalrule2" priority="10"> <lhs> <pattern name="animal" binding="animal"> <slot name="has-hair"> <constant>true</constant> </slot> </pattern> </lhs> <rhs> <function-call> <head>modify</head> <variable>animal</variable> <constant>(type mammal)</constant> </function-call> </rhs> </rule> </rulebase> (defrule AnimalRule2 (declare (salience 10))?animal <- (animal (has-hair TRUE)) => (modify?animal (type mammal)))

31 See doc