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Amzi! Logic Server for Java Applications

Amzi! Logic Server for Java Applications. References: http://www.amzi.com http://java.sun.com. Amzi! is a registered trademark and Logic Server is trademark of Amzi! Inc. Synopsis. Logic server is a software technology to access Prolog engine from host languages such as Java/C++/VB.

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Amzi! Logic Server for Java Applications

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  1. Amzi! Logic Server for Java Applications

  2. References:http://www.amzi.comhttp://java.sun.com Amzi! is a registered trademark and Logic Server is trademark of Amzi! Inc.

  3. Synopsis • Logic server is a software technology to access Prolog engine from host languages such as Java/C++/VB. • This lecture will • demonstrate Logic Server classes for Java applications. • examine some of the classes/methods that give the developer full control over the Prolog engine Note: This is NOT a course to teach Java/Prolog programming. Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  4. Target Audience • Lab Tutor for Artificial Intelligence (AI) courses • so that simple LogicServer module can be included in the syllabus of AI laboratory • Anyone who knows Java/Prolog programming but not sure how to linka back-end (Prolog) to a front-end (e.g. Java/VB/C++) Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  5. Outline • Overview: The Amzi! Logic Server (LS) Technology • Main Functions of the Logic Server • API functions that correspond to the class methods of the API • Java Class Encapsulates the Amzi! Logic Server • Entry Points • String Passing Interface • Converting Terms to Strings • Backtracking through Multiple Answers • Putting it all together: The pseudo code • Consulting Prolog Source Code • Writing Extended Predicates • LSAPI Error Handling • Software: Java2 SDK + any IDE + JRE & Prolog Engine + Amzi! LS • Configuration Tips & Programs Demo Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  6. Amzi! Logic Server(= Prolog Engine)

  7. The needs • Java doesn’t speak prolog & Prolog speaks only prolog. So, • LS technology is required to bridge the two to build intelligent applications Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  8. Overview: The Amzi! LS for Java The Java Class is implemented using the Java Native Interface (JNI). Source: www.amzi.com From right to left in the diagram, amzi.dll is the Amzi! Logic Server. amzijni.dll / libamzijni.so is the interface library that implements the Java versions of Logic Server API functions. Those, in turn are wrapped in the Java classes, LogicServer and LSException. Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  9. Why JNI? • In the case of Amzi!, the JNI is used to build a bridge to the Logic Server API, which is the external interface on the Amzi! Prolog engine. • The bridge is necessary because many of the Logic Server API functions have to be changed slightly to conform to Java parameter passing and return conventions • This is to accommodate the lack of pointer support in Java Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  10. Just Prolog ‘Listener’..will look like this Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  11. Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  12. .. Let’s pass it to Java Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  13. Greetings from Prolog, displayed in Java Env. Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  14. Main functions of the Logic Server • Two primary interfaces to the LSAPI • The Class interface is the LogicServer and LSException classes and their methods. • All the names start with 'ls'. Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  15. Java Class encapsulates the Amzi! Logic Server • For use by Java applications and applets. • A Java Class Package that encapsulates a Logic Server Engine • Methods that correspond to the Logic Server API Functions • Use of Java's exception handling for API errors Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  16. API functions that correspond to the class methods of the API • Logic Server Return Codes • Prolog Terms • String Passing Interface • Scope of Logic Server Terms • Implementing a Simple Prolog Listener • Calling Terms • Mapping Prolog Arguments to Host Variables • Making Simple Terms • Handling Varying Prolog Types • Manipulating Structures • Manipulating Lists • Asserting and Retracting Dynamic Clauses • Consulting Prolog Source • Running Multiple Engines • Writing Extended Predicates • etc. Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  17. Entry Points • The simplest host program to call Prolog clauses is one that initializes the Prolog engine, loads a Prolog logic-base, calls its main/0 predicate and then closes the Prolog engine. • To do this, the following functions are required: • Init(logic_base_name) • Initializes the Logic Server engine, allocating resources as needed. • Load(logic_base_name) • Loads the compiled Prolog .xpl file for logic_base_name. A .xpl file must always be loaded before executing any Prolog code. This is because a .xpl file includes a copy of alib.plm which implements a portion of the Prolog system software. • Main() returns TF • Calls the main/0 predicate of the loaded program. • Close() • Releases the memory and files used by the Logic Server engine. Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  18. Java Interface Example • You can write a simple host language shell that runs the a Prolog program, ipts.xpl The Knowledge Base Note: xpl = load module is needed Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  19. Look, facts are being pulled out from the .xpl module Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  20. More Examples • You can write a simple host language shell that runs the a Prolog program, hello.xpl & pets.xpl respectively. ls.Init(); ls.Load(“hello.xpl"); ls.Main(); ls.Close(); ls.Init(); ls.Load(“pets.xpl"); ls.Main(); ls.Close(); Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  21. String Passing Interface • Calling Prolog with a String Query • CallStr(query_string) returns term • Convert query_string into a Prolog term pointed to by term_ptr, and call that Prolog term. • ExecStr(query_string) returns term • Like CallStr, except it is optimized for queries that will not be backtracked through. Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  22. Example of CallStr() Use • For example, using a classic family tree Prolog application, you might want to issue the query 'sister(julie, X)' to find the sisters of julie. • If you entered this query at a Prolog listener ?- sister(julie). • Prolog would first convert that input to a term, and call it. • This is exactly what CallStr() does. Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  23. Converting Terms to Strings • TermToStr(term, string, maxlength) returns string • Convert the term to a string no longer than max-length characters. • TermToStrQ(term, string, maxlength) returns string • Convert the term to a string, using quotes for atoms and strings as necessary, so they can be used as input to Prolog again, if necessary. • StrTermLen(term) returns length • Returns the size of the string needed to hold the string representation of the term. Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  24. Backtracking through Multiple Answers • Once you have retrieved one answer from a query, you can induce Prolog backtracking and get the next answer. You can do this until there are no more answers using Redo(). • Redo() returns TF • Using the term pointed to by the previous CallStr, backtrack and redo the query. • If the query succeeds, the term is now unified based on this success and Redo() returns true, otherwise it returns false. In Prolog, to ask for more is to press/type ‘;’ at the prompt Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  25. Putting it all together • The following examples make use of this Prolog program. % a prolog source code, family.pro mother(mary,julie). mother(mary,sandy). mother(mary,ricky). mother(mary,jenny). sibling(X,Y) :- mother(P,X), mother(P,Y). Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  26. The pseudo code • This finds all of the sisters of julie and prints the full terms for each successful answer. declare TERM t declare STRING s of length 80 ls.Init() ls.Load(“family.pro") tf = ls.CallStr(&t, "sibling(julie, X)") while (tf == true) L s.TermToStr(t, s, 80) print(s) tf = ls.Redo() end while ls.Close() Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  27. Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  28. The facts (.pro) Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  29. Mapping Prolog Arguments to Host Variables (I) • One way to map Prolog arguments to host language variables is to • convert the resultant term into a string, and parse the string. • Remember that a Prolog query term is usually a structure, with a functor and a number of arguments. • For example, the query 'sibling(julie, X)' is a Prolog term/structure with the functor 'sibling' and two arguments. Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  30. Mapping Prolog Arguments to Host Variables (II) • Given this, a function that can retrieve a specific argument from a term/structure and map it into a variable is a very useful one. • GetFloatArg(term, i_arg) returns double • Gets the ith argument of term t and returns it as a host language double variable. • GetIntArg(term, i_arg) returns int • Gets the ith argument of term t and returns it as a host language double int. • GetStrtArg(term, i_arg) returns string • Gets the ith argument of term t and returns it as a host language string. • lsGetArg(term, i_arg, v_type, var) returns RC • Gets the ith argument of term t and converts it to host language type v_type and puts the result in variable var. Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  31. Making Simple Terms • In addition to the string-based functions, the API provides specific functions to make simple terms. These are: • MakeAtom(string) returns term • Returns a Prolog atom term created from the host language string. • MakeStr(term_ptr, string) returns term • Returns a Prolog string term created from the host language string. • MakeInt(term_ptr, int) returns term • Returns a Prolog integer term created from the host language integer. • MakeFloat(term_ptr, float) returns term • Returns a Prolog double precision float term created from the host language double precision float. Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  32. A prolog fact testing(1, 200000, 3.4, abc, $Universiti Tenaga Nasional$). Multiple terms are made and called from VB The codes? … next slide Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  33. Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  34. Consulting Prolog Source Code • You can also consultor re-consult source files of Prolog code. • It can be done by simply issuing a Prolog goal to consult or re-consult a file, just as you would from Prolog listener. • You can also load separate modules of compiled Prolog code if desired. • For example: • ls.ExecStr(&term, "consult(ipts)") • ls.ExecStr(&term, "reconsult(ipts)") • ls.ExecStr(&term "load(ipts)") • Note: • If you wish to use them, you must have first loaded any XPL file. This is because .xpl files are linked with alib.plm, which contains some of Amzi! Prolog's built-in predicate (such as consult, reconsult and load). Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  35. Writing Extended Predicates • To call a host language from Prolog, you must create extended predicates. • These behave just like any other built-in Prolog predicates, except you have written them. • Note: Only host languages that support p_______ or virtual machine extensions, such as C/C++, Delphi or Java, can be used for implementing extended predicates. Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  36. Adding extended predicate • Define a host language function that will implement the predicate. • Inform the Logic Server during initialization of • the name and arityof the Prolog predicate • the address of the host language function that implements it. Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  37. Initializing the Extended Predicates • Once you have defined a number of functions, you need to let the Logic Server know about them. • This is done after the call to Init in one of three different ways. • AddPred(functor, arity, function_ptr) • Maps the Prolog predicate of functor/arity to the host language function. Must be called once for each extended predicate. • InitPreds(pred_table_ptr) • Uses a host language table that maps Prolog predicates to functions. Called once to initialize all of the predicates in the table. • InitLSX(ptr) • Causes the Logic Server to check the .cfg file for a lsxload parameter. It then automatically loads any .LSXs (DLLs containing extended predicates) listed in the .cfg file. Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  38. Implementing Extended Predicates • Java, like C/C++, Delphi and VB 5.0 (and later), can be used to implement custom extended predicates to the Prolog language. • These custom extensions give the Prolog code the ability to directly access anything Java can access. • The Java methods that implement extended predicates, must be declared as returning type boolean, and as public. • If your extended predicate is in a package, then the package name must be included in the class name, delimited by forward slashes, to AddPred as follows: • ls.AddPred("extpred", 1, "javapkg/jprolog", "extpred", this); Note: Extended predicate definitions must always be added after calling InitLS and before calling LoadXPL. Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  39. ‘prompt’ is a Prolog Extended Predicate (i.e. a Java Method) Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  40. Register it to Amzi! The method is implemented here Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  41. output Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  42. LSAPI Error Handling • When used from Java or another object-oriented language, all errors from LSAPI functions are thrown using the LSException class. • Class Error Handling • When an exception occurs in the engine, and the engine was accessed from the LogicServer class, then an instance of LSException is thrown. • When catching Logic Server exceptions, it is better to catch a reference to the exception object. • For example: • try { // Logic Server stuff } catch(LSException &e) { // recovery stuff } Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  43. Java Meets Prolog Program extensions that needed (.java, .class, .pro, .plm, .xpl, &.jpx) Software dependent

  44. Java and Prolog • Java is designed to be an object oriented language for deploying secure, multithreaded network applications (both clients and servers). • Prolog is ideal for building intelligent components, expert systems and logic-bases. • In combination, Java and Prolog are a good pair for delivering useful intelligent applications. Back-end handles reasoning/searching/etc., while the front-end does some numerical processing and prepares the GUI components. Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  45. Software Download &Configuration Tips Refer www.amzi.com for “How to install the Logic Server as a Java class”. You can download Sun's Development Kit (e.g. SDK) from http://developers.sun.com/ Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  46. Configuration • To use the Java Class, you must make the following files accessible to the calling environment: • Amzi! Dynamic/Shared Library • The Amzi! Logic Server, amzi.dll or libamzi.so, and the Amzi! Java interface, amzijni.dll, must be in your PATH. • Amzi! Java Classes • The amzi/ls directory structure, containing the amzi.ls.* package must be accessible via your CLASSPATH. You can do this by adding amzi/lsapis/java20 to your CLASSPATH Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  47. Tips • Classpath (etc.) settings and inclusions of Amzi! LS classes & all DLLs for VB/C++/Java are different. • Front-end modules developed using Java is greatly depended on the (GUI) Tools you use. • E.g. the way JBuilder sees it is different from the way Eclipse/Visual Safe/NetBean/Command line can recognize it. Alicia Tang, Dept. of Computer Science, COIT, UNITEN

  48. Test this:Amzi! Hello sample for Java(before you begin to use other LS commands) • To make sure the Amzi! Java interface is ready to use, run the Amzi! Hello sample for Java. • To build the Hello program from Java, first open a 'DOS' window and change to the sample directory containing Hello.java. • To compile it, type: • javac Hello.java • This will produce Hello.class which is simply run by typing: • java Hello Alicia Tang, Dept. of Computer Science, COIT, UNITEN

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