Syntactic Methods - Anomalies

Anomalies

There are four main types of anomaly:

• Redundancies – A chunk of the graph is redundant if its terminals can be reached if the chunk is removed from the graph
• Conflicts – A system contains conflicts if the same inputs can imply different outputs
• Circularities – A loop in the graph indicates a circularity in the system
• Deficiencies – A chunk is deficient if a subset of inputs leads to no terminals

While anomalies often point to defects, they can just as easily reflect normal intended functionality in the system. It is up to the developer to look into anomalies in order to determine whether they are clues to problems or simply false alarms.

By creating a visual directed graph of a system, there are several obvious visual flags that indicate the above anomalies:

• a sub-graph with no input is probably missing something important;
• while looking at the transitive closure of a system (all nodes downstream from a node), a node in its own transitive closure indicates a circularity;
• while looking at the transitive closure of a system, subsumption between pairs of rows indicates redundancy;
• conflicts are somewhat more difficult as they become more semantic than syntactic.

When formal methods prove too costly, a system can be checked solely on its syntax. This is not as thorough, as it only looks at a system on a surface level. However, it does give a developer many clues as to where a system's defects may lie.