this paper we describe a statically typed XML processing language called XDuce (o#cially pronounced "transduce"). XDuce is a functional language whose primitive data structures represent XML documents and whose types---called regular expression types---correspond to document schemas. The motivating principle behind its design is that a simple, clean, and powerful type system for XML processing can be based directly on the theory of regular tree automata

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Many data-intensive applications dynamically construct queries in response to client requests and execute them. Java servlets, e.g., can create string representations of SQL queries and then send the queries, using JDBC, to a database server for execution. The servlet programmer enjoys static checking via Java's strong type system. However, the Java type system does little to check for possible errors in the dynamically generated SQL query strings. Thus, a type error in a generated selection query (e.g., comparing a string attribute with an integer) can result in an SQL runtime exception. Currently, such defects must be rooted out through careful testing, or (worse) might be found by customers at runtime. In this paper, we present a sound, static, program analysis technique to verify the correctness of dynamically generated query strings. We describe our analysis technique and provide soundness results for our static analysis algorithm. We also describe the details of a prototype tool based on the algorithm and present several illustrative defects found in senior software-engineering student-team projects, online tutorial examples, and a realworld purchase order system written by one of the authors.

Server-side programming is one of the key technologies that support today's WWW environment. It makes it possible to generate Web pages dynamically according to a user's request and to customize pages for each user. However, the flexibility obtained by server-side programming makes it much harder to guarantee validity and security of dynamically generated pages.

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We survey work on statically type checking XML transformations, covering a wide range of notations and ambitions. The concept of type may vary from idealizations of DTD to full-blown XML Schema or even more expressive formalisms. The notion of transformation may vary from clean and simple transductions to domain-specific languages or integration of XML in general-purpose programming languages. Type annotations can be either explicit or implicit, and type checking ranges from exact decidability to pragmatic approximations. We characterize

We describe the summary graph lattice for dataflow analysis of programs that dynamically construct XML documents. Summary graphs have successfully been used to provide static guarantees in the JWIG language for programming interactive Web services. In particular, the JWIG compiler is able to check validity of dynamically generated XHTML documents and to type check dynamic form data. In this paper we present summary graphs and indicate their applicability for various scenarios. We also show that the expressive power of summary graphs is similar to that of the regular expression types from XDuce, but that the extra structure in summary graphs makes them more suitable for certain program analyses.

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Abstract. In this paper we present the iData Toolkit. It allows programmers to create interactive, dynamic web applications with state on a high level of abstraction. The key element of this toolkit is the iData element. An iData element can be regarded as a self-contained object that stores values of a specified type. Generic programming techniques enable the automatic generation of HTML-forms from these types. These forms can be plugged into the web application. The iData elements can be interconnected. Complicated form dependencies can be defined in a pure functional, type safe, declarative programming style. This liberates the programmer from lots of low-level HTML programming and form handling. We illustrate the descriptive power of the toolkit by means of a small, yet complicated example: a project administration. The iData Toolkit is an excellent demonstration of the expressive power of modern generic (poly-typical) programming techniques.

In this paper we introduce the iTask system: a set of combinators to specify work flows in a pure functional language at a very high level of abstraction. Work flow systems are automated systems in which tasks are coordinated that have to be executed by humans and computers. The combinators that we propose support work flow patterns commonly found in commercial work flow systems. Compared with most of these commercial systems, the iTask system offers several advantages: tasks are statically typed, tasks can be higher order, the combinators are fully compositional, dynamic and recursive work flows can be specified, and last but not least, the specification is used to generate an executable web-based multi-user work flow application. With the iTask system, useful work flows can be defined which cannot be expressed in other systems: work can be interrupted and subsequently directed to other workers for further processing. The implementation is special as well. It is based on the Clean iData toolkit which makes it possible to create fully dynamic, interactive, thin client web applications. Thanks to the generic programming techniques used in the iData toolkit, the programming effort is reduced significantly: state handling, form rendering, user interaction, and storage management is handled automatically. The iTask system allows a task to be regarded as a special kind of persistent redex being reduced by the application user via task completion. The combinators control the order in which these redexes are made available to the application user. The system rewrites the persistent task redexes in a similar way as functions are rewritten in lazy functional languages.