Towards a Java Framework for Knowledge Representation and Inference

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1 Towards a Java Framework for Knowledge Representation and Inference Adrian GIURCA University of Craiova, Faculty of Mathematics and Computer Science giurca@inf.ucv.ro Abstract. The Knowledge Representation Package consist of a framework that implement several kinds of processing engines. The framework using a data structure based on the Blackboard pattern [2], is written in Java and has three main components: knowledge representation, knowledge repository and inference engine. It can be used for make reasoning in semantic networks, frames or rule based systems. In inference we propose an uniform representation for knowledge using rules. The inference engine allow to construct all first order logic constructs. AMS Classification. Primary: 68R99, Secondary: 68T30 Keywords: knowledge representation, inference, OOP, Java, blackboard pattern. 1 Motivation It is probably safe to say that we will never have enough computing power to solve the problems people really want to solve. These problems are complex and multifaced, often requiring solutions that employ several kinds of representation and reasoning mechanisms simultaneously. As computers become more powerful and applications become more sophisticated, the complex problems of yesterday are understood and solved, but there are always new problems that are even more complex on the horizon. It is a never ending cycle. What is needed in this kind of environment is a set of tools that enable software developers the ability to represent knowledge about complex problems in the application and to apply multiple reasoning mechanisms to that knowledge in order to derive solutions. These tools must be designed in a such way that they can evolve over long periods of time as software developers improve our understanding of the problems they seek to solve and as their computing environments become more powerful. The study of Artificial Intelligence (AI) and Object-Orientation (OO) provide the technology for creating the right king of tools for solving complex problems. AI provides the means through wich applications represent knowledge about complex problems and reason about that knowledge. OO provides the means through which application components can be constructed so they are reusable and maintainable. The complexity of the AI components are managed by the powerful abstraction and layering facilities of OO language and methodologies.

2 2 Adrian GIURCA OO technology also can be used to construct applications that can evolve over time without succumbing to architectural entropy. Object-oriented architectures, commonly known as frameworks, allow Ai components to be built in a such a way that: they can rapidly integrated into applications with a minimum amount of effort. they can be reused in multiple applications, eliminating the need for custombuilt AI applications they retain their architectural integrity with less effort than AI subsystems built using other types of architectures (functional, procedural, etc), allowing for coherent system evolution. 2 The Blackboard Pattern Our design choice is the Blackboard architectural pattern [2]. In the following we make a short description of the Blackboard pattern to motivate or choice. The idea behind the Blackboard architecture is a collection of independent programs that work cooperatively on a common data structure. Each program is specialized for solving a particular part of the overall task, and all programs work together on the solution. These specialized programs are independent of each other. They do not call each other, nor is there a predetermined sequence for their activation. Instead, the direction taken by the system is mainly determined by the current state of progress. A central control component evaluates the current state of processing and coordinates the specialized programs. This data-directed control regime makes experimentation with different algorithms possible, and allows experimentally-derived heuristics to control processing. The structure is presented in figure Blackboard Component The blackboard component provides a central data store for all hypotheses created during analysis. The main functions are: Stores current state of the solution space Stores all control data Delivers requested data to the operating knowledge sources Since the Blackboard is essentially a shared memory repository, synchronization techniques may be required for multiple writers and readers (multiple knowledge sources) 2.2 Knowledge Source Component Knowledge Sources are separate and independent systems that individually solve parts of the problem in piecemeal fashion. Each knowledge source has a certain area of expertise, or at least focus. In this they can be seen as specialists. Knowledge sources obtain data from the blackboard, and return hypotheses developed from the data. Each hypothesis is made up of things like:

3 Towards a Java Framework for Knowledge Representation and Inference 3 Fig. 1. Blackboard Pattern [2]

4 4 Adrian GIURCA an abstraction level: the distance from the input an estimated confidence factor a time interval covered by the hypothesis Also, knowledge sources are reactive in the sense that they react to changes in the problem domain as rendered by the blackboard. 2.3 Control Component The controller runs continually monitoring the state of the blackboard, and will end processing whenever an acceptable solution is found. The controller uses heuristics to develop alternate strategies according to the current state of the blackboard, and schedules knowledge sources based on the current strategy. He activates each knowledge source when its scheduled time has arrived. The controller can query a knowledge source to determine its estimated probability of success or its estimated time of execution, and can update its strategy accordingly, often according to a user-delivered desired confidence level. Often, a complete search of the solution space is not feasible. In this case, algorithms must be developed that filter significant information from noise. A data-directed (but not driven) mechanism of coordinating or non coordinating subsystems uses opportunistic problem solving to provide some solution. Such opportunistic analysis with multiple algorithms of various talents and biases may produce heuristics that can be used to refine searches. Using this pattern we have the followings advantages: Fault tolerant. Reusable. Allows for experimentation. Potential parallel execution, which can greatly enhance cost-effectiveness over traditional message-based systems. There exist also several disadvantages: Low testability. Solutions are variable in terms of quality and not guaranteed. Usually inefficient, costly in terms of execution. Based on this pattern, our framework has three different views organized around the type of functionality provided by the components in each view and their collaborations. These views are: Knowledge Representation Knowledge Repository Inference Engine The following sections will describe all of this views.

5 Towards a Java Framework for Knowledge Representation and Inference 5 3 Knowledge Representation In the study of AI, knowledge representation is the combination of data structures and interpretive procedures that, if used correctly, will lead to knowledgeable behavior (see [1]). The types of knowledge represented in AI systems include: objects - AI systems typically reason about objects in the world around us. relationships - Real world objects interact with each other. These interactions are characterized by relationships. events - We know about actions and events in the world and how they affect objects and their relationships. instructions - Some types of knowledge describe how to do things. This may involves scripts that can be followed by computers or people. meta-knowledge - We also need to model knowledge about what we know. We may need to know about the reliability of an information source or we may need to be cognizant of out limitations when observing the world. Given the above description of knowledge representation in AI terms, knowledge representation in object-oriented terms is the reification of domain specific knowledge into objects that can be manipulated by the framework and the clients of the framework. In an object-oriented system, all types of knowledge is represented by objects or methods of objects. In our framework, the basic knowledge ( atom of knowledge ) is an object that implement the AtomKnowledge interface. This interface provides methods for identifying the knowledge atom and serves as the placeholder whereby domain specific objects implementing the AtomKnowledge interface can be managed. The following interfaces and classes are designed: AtomKnowledge - This interface extends the Observable interface (see the Observer pattern) by declaring additional methods for knowledge atom identification. Blackboard objects manage knowledge atoms through the AtomKnowledge interface. AbstractAtomKnowledge - this abstract class partially implements the AtomKnowledge interface and assimilates the Subject mixin class. Subclasses of the AbstractAtomKnowledge abstract class must provide the remaining functionality and structure to fully implement the AtomKnowledge interface. ConcreteKnowledge - This concrete class represents a programmer defined atom knowledge. This class extends the AbstractAtomKnowledge abstract class by providing some kind of domain-specific functionality and structure that models an atom of knowledge for that domain. Several examples will be given in the next sections to illustrate how to extend the AbstractAtomKnowledge class to create different types of knowledge atoms.

6 6 Adrian GIURCA Fig. 2. Knowledge Representation 3.1 Semantic Network The first class in this example (SemanticLink) represents the links in a semantic network. The SemanticLink class has a name to identify the link type, a description which contains information about what the link represents, and a SemanticNode node which makes up the other end of the link. Example 1 (A Semantic link). package semanticnetwork; public class SemanticLink{ private String label; private String description = ""; private SemanticNode node; public SemanticLink(String label, String description, SemanticNode node){ setname(label); setdescription(description); setnode(node); public String getlabel(){

7 Towards a Java Framework for Knowledge Representation and Inference 7 return label; public String getdescription(){ return description; public SemanticNode getnode(){ return node; public String tostring(){ if (null!= node){ return "["+label+","+ "description"+","+ node.tostring()+"]"; else{ return null; private void setlabel(string label) throws IllegalArgumentException{ if (null!= label){ this.label = label; else{ throw new IllegalArgumentException("label cannot be null!"); private void setdescription(string description){ if (null!= description){ this.description = description; private void setnode(semanticnode node) throws IllegalArgumentException{ if (null!= node){ this.node = node; else{ throw new IllegalArgumentException("node cannot be null!");

8 8 Adrian GIURCA The second class in the example (SemanticNode) represents the nodes in a semantic network. SemanticNode extends the AbstractAtomKnowledge abstract class by adding a description which contains information about what the node represents and a list of links which represent relationships between other nodes. SemanticNode provides methods for accessing its information, including methods for accessing the individual links in the link list or iterating through the entire list. Example 2 (A Semantic Node). package semanticnetwork; import java.util.*; public class SemanticNode extends AbstractAtomKnowledge{ private String description; private List links; public SemanticNode(String description, List links){ this.description = description; setlinks(links); public List getlinks(){ return links; public String getdescription(){ return description; public int getnooflinks(){ return links.length; public SemanticLink getlink(int index){ if (index <= links.length-1){ return (SemanticLink)links.get(index); else{ return null; public List getlinks(string label){ List result = new ArrayList(); Iterator i = links.iterator();

9 Towards a Java Framework for Knowledge Representation and Inference 9 while (i.hasnext()){ SemanticLink link = (SemanticLink)i.next(); if (link.getlabel() == label){ result.add(link); return result; public List getlinkednodes(){ List result = new ArrayList(); Iterator i = links.iterator(); while (i.hasnext()){ SemanticLink link = (SemanticLink)i.next(); result.add(link.getnode()); return result; public boolean setlink(semanticlink link){ return this.links.add(link); private void setlinks(list links){ Iterator i = links.iterator(); while (i.hasnext()){ SemanticLink link = (SemanticLink)i.next(); this.links.add(link); 3.2 Frames Frames are similar to semantic networks. In fact, frames can be used to model semantic networks if they are structured in the right way. FrameData is an interface class that combines the Clonable and Countable interfaces together to provide the base interface of frame data objects. FrameBehavior is similar to FrameData but it combines the Clonable, Countable, and Executable interface together to provide the base interface of frame behavior objects. The Frame class is created by implementing the FrameData interfaces and extending the AbstractAtomKnowledge abstract class. Frame contains a map of frame data objects and a map of frame behavior objects. Methods for accessing individual objects in either map are provided as well as methods for iterating over the whole map.

10 10 Adrian GIURCA Fig. 3. The Structure of Frames The knowledge representation facilities provided by the framework instantiate the Observer design pattern described in [3]. The Observer design pattern provides a means for notifying dependents of knowledge atoms of state changes. In the figure 4 we present the structure of the framework notifications. 4 Knowledge Repository A blackboard architecture also serves as a repository of knowledge in addition to representing individual atoms of knowledge. This repository is often called the blackboard or work area. The blackboard is the common area where knowledge is read, written, and manipulated during the process of inference. The structure is presented in the figure 5. 5 Inference Engine Our inference engine enables the flexible construction of inference networks based on rules for a wide variety of domains. The engine is possible to be extended for other types of mechanisms. Formally, the inference engine allow to construct all first order logic constructs. Using the inference engine we have the following benefits:

11 Towards a Java Framework for Knowledge Representation and Inference 11 Fig. 4. Object Notification Modularity. Groups of related rules can be interchanged without effecting the overall structure of the system. They behave much like independent pieces of knowledge. Uniformity. Imposes a uniform structure on the knowledge modelled by the inference network. Since all knowledge must be encoded in a rule form, it can often be more easily understood. Naturalness. Rules are a common way of expressing what to do in a predetermined situations. However, there are some liabilities: Inefficiency. Program execution is much more inefficient than in procedural programs. Non-obvious flow control. It is hard to follow the flow of control through the execution of inference networks. Algorithmic knowledge is not expressed naturally in inference networks. References 1. Barr, Avron and Edward A. Feigenbaum (eds.) The Handbook of Artificial Intelligence, vol1, pp , Adison-Wesley Inc Buschmann, Frank, Regine Meunier, Hans Rohnert, Peter Sommerland and Michael Stal, Pattern Oriented Software Architecture: A System of Patterns, pp.71-95, John Willey & Sons Ltd., 1996.

12 12 Adrian GIURCA Fig. 5. Knowledge Repository

13 Towards a Java Framework for Knowledge Representation and Inference Gamma Erich, Richard Helm, Ralph Johnson and John Vlissides, Design Patterns: Elements of Reusable Object-Oriented Software, pp , , , , Addison wesley, xml.com. (2002a).

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