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2. STATE OF THE ART AND RELATED WORK 2.4. Representation of Configuration Files in a Generic Syntax 2.3.2 JavaCC The Java Compiler Compiler (JavaCC) [Pro09] is a tool that reads a grammar specification and converts it to a Java program that can recognize matches to the grammar. In addition to the parser generator itself, JavaCC provides other standard capabilities related to parser generation such as tree building, actions, debugging, etc. JavaCC generates top-down parsers (i.e., start at the root of the derivation tree, picks a production and tries to match the input tokens [oM]), declares the lexical and grammar specifica- tions in one file, making grammars easier to read and maintain, supports semantic lookahead, uses the Extended Backus-Naur Form (i.e., operators *, + and ?) and supports error recovery in two forms: shallow recovery and deep recovery. In shallow recovery, if an input token does not match any production, it is possible to move to the next desired token (e.g., semicolon). Deep recovery is similar to the shallow recovery, but also allows to recover from an error inside a production, which is impossible resorting to shallow recovery alone. 2.4 Representation of Configuration Files in a Generic Syntax The concept of generic syntax refers to a language-independent syntax used in the process of automatic application configuration. The generic syntax is used to abstract the configuration files from their original languages. When a configuration file is represented in a generic syntax, another independent entity which recognizes that syntax is able to manipulate the file without having knowledge of what the original syntax was, or what application uses that file. The chosen generic syntax must provide a practical way to traverse and manipulate files. Furthermore, it must be widely supported and well documented. Its software license must also allow it to be used freely. Considering the prievous requirements, the chosen syntax was the eXtensible Markup Lan- guage (XML) since it is a broadly adopted and supported standard. XML allows for the struc- turing of configuration files in a way that makes them easily manipulable and traversable. Some available implementations of XML parsers were identified in many programming languages. The criteria to choose from an XML parser implementation includes factors such as the programming languages it is available on and what it allows the user to do resulting data structure from the parse. Since the programming language used to develop the tool is going to be Java, two major XML parser implementations in Java were considered: the Simple API for XML (SAX) and the Domain Object Model (DOM). Following is a brief description of both. Simple API for XML The Simple API for XML (SAX) is an Application Programming Interface (API) for XML in Java, although it is available in many other programming languages. It is event-driven: it reads from a stream and reacts when processing instructions, elements, comments and text. 18
2. STATE OF THE ART AND RELATED WORK 2.4. Representation of Configuration Files in a Generic Syntax Being event-oriented, SAX does not implement a representation of the document in memory and, therefore, memory accesses are seldom in quantity. This leads to some memory inde- pendence and fairly good memory consumption ratings, also excelling in large files parsing. SAX parses in an uni-directional way since it does not allow previously read data to be read again, without restarting the parser. This consists on a problem when a whole XML document must be in memory in order to be properly parsed, as SAX requires the user to start the parsing again to get values previously obtained. Domain Object Model DOM is a cross-platform and language-independent interface for creating and manipulating XML documents in memory. It is a World Wide Web Consortium (W3C) standard. It loads an XML document to memory and allows for dynamic access to it, allowing for bi-directional parsing. DOM represents an XML document in memory in a tree-like structure. Furthermore, it is very well supported in many programming languages, including Java. Since DOM keeps a document in memory after it is parsed, a drawback is the time spent to parse a big file on the grounds that many memory allocation requests might sum up to a considerable time. 19
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Bibliography [Ama09] Amazon. Amazon
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BIBLIOGRAPHY [Sol09a] Evolve Space
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Dissertaç ˜ao de Mestrado Mestrado em Engenharia Informática Jo ...

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