Dissertaç ˜ao de Mestrado Mestrado em Engenharia Informática Jo ...

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 pro-
duction 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 cho-
sen 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.
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