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Chapter 4. Measuring Evolving Software
Once a pattern was established to identify specific libraries, we used the
same pattern across all projects in our data set. The regular expression
based external library identification lists created for each software system
in our data set was also manually checked to ensure that it was not
selecting classes that can be considered to be part of the core software
system (cf. Section 3.6 for a description of core software system).
In the final stage of this step, we determined the release date for the
version from the JAR files that have been determined to be part of the
core software system. All Java archives contain a Manifest file that is
created as part of the JAR construction process. We use the creation
date timestamp of this Manifest file to determine the release date for
the Version. Where a version contains multiple JAR files, we apply
the maximum function and take the latest date to represent the release
date for the entire version. This was needed since certain projects tend
to constructed JAR files for their distribution over multiple days rather
than build it all on a single date.
Once the release date for a version was established, we ordered all versions
by release date and compute the Release Sequence Number (RSN)
for each version. We started the RSN numbers at 1 for the oldest version
and incremented it by 1 for each subsequent version.
4.5.2 Class Metric Extraction
After the classes files are extracted from the JAR file, we process each
class file using ASM, a Java Bytecode manipulation framework [9], in
order to extract information from the compiled Java class (Table 4.1
highlights the information that is available to be extracted from a compiled
Java class). In this step we compute direct measures such as
the Number of Fields for a class as well as extracting its additional information
such as the fully qualified class name (i.e. class name includes
the package name; an example of a fully qualified class name is
java.lang.String, where java.lang is the package name).
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