SEKE 2012 Proceedings - Knowledge Systems Institute

C. Correctness of configuration files
We define correctness of configuration files in order to check
configuration files. First, we define a configuration file which
is represented using configuration file model.
CFile = { (n,v)| n ∈ PN, v ∈ PV }
A configuration file (CFile) is defined as set of combination
of setting item and parameter.
Second, we define four properties in order to define correctness
of configuration files.
• constraint on combination of setting item and parameter
s conf ⇔∀(a, b) ∈ CFile. b ∈ Conf(a)
This constraint means that combinations of item and
parameter which are written in a configuration file have
to be defined in configuration file model.
• constraint on dependency between combinations of setting
item and parameter
s rel ⇔∃x y. (x, y) ∈ Rel ∧ x ∈ CFile → y ∈ CFile
This constraint means that if a combination of setting
item and parameter is written in a configuration file and
requires other combinations, required combinations have
to be written in the configuration file.
• constraint on relation between requirements
This constraint means that if an element of requirement
is chosen and requires other elements of requirement,
required elements have to be chosen.
• constraint on relations between requirement and configuration
file
s req ⇔∀r ∈ CR. Req(r) ∈ CFile
This constraint means that if a requirement is chosen and
relates to combinations of setting item and parameter,
the combinations of setting item and parameter have to
be written in a configuration file.
Correctness of CFile is defined that CFile satisfies above
properties.
V. METHOD FOR MAKING CONFIGURATION FILES
The workflow of our method is shown in Fig. 3.
Fig. 3.
Workflow of the Method
We already defined configuration file model and correctness
of configuration files. Properties which are used in order to
prevent configuration file errors are organized in configuration
file model. However, the properties are not easy to apply
check configuration files because there is a gap between
configuration file model and configuration file description.
One solution is that to describe configuration file model and
configuration files in common description method. Therefore,
we use the feature diagram to describe configuration file model
and configuration files. Besides, constraints of the feature
diagrams are used to check correctness of configuration file.
A. Configuration model
Configuration model is a model that configuration file model
is described using the feature diagram. Configuration model
consists of requirement model which is a feature diagram
of requirement, config model which is a feature diagram
of configuration file, and correspondence relations between
feature diagrams.
A configuration model is described as following method.
Requirement model is described by analyzing commonality
and variability of functions of application. Config model is
described by analyzing candidates of combinations of setting
item and parameter. Combinations of setting item and parameter
have some patterns. So, we analyzed syntax of httpd.conf,
which is configuration file of Apache web server, and extracted
five patterns of combinations. The patterns are as follows.
• Pattern 1. setting item needs one parameter which is
selected from set of candidates of parameter.
• Pattern 2. setting item needs some parameters which are
selected from set of candidates of parameter.
• Pattern 3. setting item needs two parameters which are
selected from different set of candidates of parameter.
• Pattern 4. setting item needs one parameter which is selected
from candidates of parameter and some parameters
which are selected from different set of candidates of
parameter.
• Pattern 5. setting item does not need parameter.
The above patterns are used for constraints when combinations
of setting item and parameter are chosen. Besides,
the patterns are described using feature diagram. In order to
describe the patterns, our method uses Mandatory, Optional,
Alternative and Or relations of the feature diagram. Each
pattern is described as follows.
• Pattern 1 is described by Alternative relation.
• Pattern 2 is described by Or relation.
• Pattern 3 is described by two Alternative relations.
• Pattern 4 is described by Alternative and Or relation.
• Pattern 5 is described only parent.
Additionally, there are dependency relations of combinations
of setting item and parameter. These relations are able
to describe by composition rules of the feature diagram.
An example of configuration model is shown in Fig. 4. In
Fig. 4, the upper side diagram is requirement model and the
under side diagram is config model. Dotted line arrows from
requirement model to config model represent correspondence
relations between requirement model and config model.
B. Error detection
We deal with checking correctness of configuration files as
checking validity of chosen features from configuration model.
Therefore, our consistency checking method checks whether
set of features which are chosen from configuration model
is an instance. An instance means a set of features which
satisfies constraints of the feature diagram. In order to detect
674