Elnar Hajiyev

CodeQuest : scalable source code queries with datalog

Source code querying tools allow programmers to explore relations between different parts of the code base. This paper describes such a tool, named codeQuest. It combines two previous proposals, namely the use of logic programming and database systems. As the query language we use safe Datalog, which was originally introduced in the theory of databases. That provides just the right level of expressiveness; in particular recursion is indispensable for source code queries. Safe Datalog is like Prolog, but all queries are guaranteed to terminate, and there is no need for extra-logical annotations. Our implementation of Datalog maps queries to a relational database system. We are thus able to capitalise on the query optimiser provided by such a system. For recursive queries we implement our own optimisations in the translation from Datalog to SQL. Experiments confirm that this strategy yields an efficient, scalable code querying system.

Keynote Address: .QL for Source Code Analysis

Many tasks in source code analysis can be viewed as evaluating queries over a relational representation of the code. Here we present an object-oriented query language, named .QL, and demonstrate its use for general navigation, bug finding and enforcing coding conventions. We then focus on the particular problem of specifying metrics as queries.

.QL: Object-Oriented Queries Made Easy

These notes are an introduction to .QL, an object-oriented query language for any type of structured data. We illustrate the use of .QL in assessing software quality, namely to find bugs, to compute metrics and to enforce coding conventions. The class mechanism of .QL is discussed in depth, and we demonstrate how it can be used to build libraries of reusable queries.

Semantics of static pointcuts in aspectJ

In aspect-oriented programming, one can intercept events by writing patterns called pointcuts. The pointcut language of the most popular aspect-oriented programming language, AspectJ, allows the expression of highly complex properties of the static program structure.We present the first rigorous semantics of the AspectJ pointcut language, by translating static patterns into safe ( i.e. range-restricted and stratified) Datalog queries. Safe Datalog is a logic language like Prolog, but it does not have data structures; consequently it has a straightforward least fixpoint semantics and all queries terminate.The translation from pointcuts to safe Datalog consists of a set of simple conditional rewrite rules, implemented using the Stratego system. The resulting queries are themselves executable with the CodeQuest system. We present experiments indicating that direct execution of our semantics is not prohibitively expensive.

Aspects for trace monitoring

A trace monitor observes the sequence of events in a system, and takes appropriate action when a given pattern occurs in that sequence. Aspect-oriented programming provides a convenient framework for writing such trace monitors. We provide a brief introduction to aspect-oriented programming in AspectJ. AspectJ only provides support for triggering extra code with single events, and we present a new language feature (named tracematches) that allows one to directly express patterns that range over the whole current trace. Implementing this feature efficiently is challenging, and we report on our work towards that goal. Another drawback of AspectJ is the highly syntactic nature of the event patterns, often requiring the programmer to list all methods that have a certain property, rather than specifying that property itself. We argue that Datalog provides an appropriate notation for describing such properties. Furthermore, all of the existing patterns in AspectJ can be reduced to Datalog via simple rewrite rules. This research is carried out with abc, an extensible optimising compiler for AspectJ, which is freely available for download.

CodeQuest: querying source code with datalog

We describe CodeQuest, a system for querying source code. It combines two previous proposals, namely the use of logic programming and database system. Experiments (on projects ranging from 3KSLOC to 1300KSLOC) confirm that for this application, a query language based on DataLog strikes the right balance between expressiveness and scalability.

Improve software quality with SemmleCode: an eclipse plugin for semantic code search

Navigate code, find bugs, compute metrics, check style rules, and enforce coding conventions in Eclipse with SemmleCode. SemmleCode is a new free Eclipse plugin that allows you to phrase these tasks as queries over the codebase - it thus takes the search facilities in Eclipse to a whole new level. A large library of queries for common operations is provided, including metrics and Java EE style rules. Query results can be displayed as a tree view, a table view, in the problem view, as charts or graphs, all with links to the source code.

Datalog as a pointcut language in aspect-oriented programming

AspectJs pointcut language is complex, yet often not expressive enough to directly capture a desired property. Prolog has been suggested as an alternative, but Prolog queries may not terminate, and they tend to be verbose. We solve expressiveness, termination and verbosity by using Datalog plus rewrite rules.

Object-oriented queries over software systems: (abstract of invited talk)

Code queries are useful for enforcing coding conventions, navigating a large code base, and for identifying locations to refactor. The program understanding community has long advocated the use of a relational database to facilitate such code queries [3, 9]. While the idea has found some uptake in industry [2, 11], relational queries over code have not yet found widespread use.

Aspects and data refinement

We give an introduction to aspect-oriented programming from the viewpoint of data refinement. Some data refinements are conveniently expressed via aspects. Unlike traditional programming language features for data refinement, aspects conceptually transform run-time events, not compile-time programs.