Christian Kirkegaard

Static analysis of XML transformations in Java

XML documents generated dynamically by programs are typically represented as text strings or DOM trees. This is a low-level approach for several reasons: 1) traversing and modifying such structures can be tedious and error prone, 2) although schema languages, e.g., DTD, allow classes of XML documents to be defined, there are generally no automatic mechanisms for statically checking that a program transforms from one class to another as intended. We introduce XACT, a high-level approach for Java using XML templates as a first-class data type with operations for manipulating XML values based on XPath. In addition to an efficient runtime representation, the data type permits static type checking using DTD schemas as types. By specifying schemes for the input and output of a program, our analysis algorithm will statically verify that valid input data is always transformed into valid output data and that the operations are used consistently.

Static analysis for java servlets and JSP

We present an approach for statically reasoning about the behavior of Web applications that are developed using Java Servlets and JSP. Specifically, we attack the problems of guaranteeing that all output is well-formed and valid XML and ensuring consistency of XHTML form fields and session state. Our approach builds on a collection of program analysis techniques developed earlier in the JWIG and Xact projects, combined with work on balanced context-free grammars. Together, this provides the necessary foundation concerning reasoning about output streams and application control flow.

A Runtime System for XML Transformations in Java

We show that it is possible to extend a general-purpose programming language with a convenient high-level data-type for manipulating XML documents while permitting (1) precise static analysis for guaranteeing validity of the constructed XML documents relative to the given DTD schemas, and (2) a run-time system where the operations can be performed efficiently. The system, named XACT, is based on a notion of immutable XML templates and uses XPath for deconstructing documents. A companion paper presents the program analysis; this paper focuses on the efficient runtime representation.

Exploiting schemas in data synchronization

Increased reliance on optimistic data replication has led to burgeoning interest in tools and frameworks for synchronizing disconnected updates to replicated data. We have implemented a generic synchronization framework, called Harmony, that can be used to build statebased synchronizers for a wide variety of tree-structured data formats. A novel feature of this framework is that the synchronization process—in particular, the recognition of conflicts—is driven by the schema of the structures being synchronized. We formalize Harmony’s synchronization algorithm, state a simple and intuitive specification, and illustrate how it can be used to synchronize trees representing a variety of specific forms of application data, including sets, records, and tuples.