Anders Sandholm

Mona: Monadic Second-Order Logic in Practice

The purpose of this article is to introduce Monadic Second-order Logic as a practical means of specifying regularity. The logic is a highly succinct alternative to the use of regular expressions. We have built a tool MONA, which acts as a decision procedure and as a translator to finite-state automata. The tool is based on new algorithms for minimizing finite-state automata that use binary decision diagrams (BDDs) to represent transition functions in compressed form. A byproduct of this work is an algorithm that matches the time but improves the space of Sieling and Wegeners algorithm to reduce OBDDs in linear time.

A type system for dynamic Web documents

Many interactive Web services use the CGI interface for communication with clients. They will dynamically create HTML documents that are presented to the client who then resumes the interaction by submitting data through incorporated form fields. This protocol is difficult to statically type-check if the dynamic documents are created by arbitrary script code using printf-like statements. Previous proposals have suggested using static document templates which trades flexibility for safety. We propose a notion of typed, higher-order templates that simultaneously achieve flexibility and safety. Our type system is based on a flow analysis of which we prove soundness. We present an efficient runtime implementation that respects the semantics of only well-typed programs. This work is fully implemented as part of the <bigwig> system for defining interactive Web services.

Distributed safety controllers for web services

We show how to use high-level synchronization constraints, written in a version of monadic second-order logic on finite strings, to synthesize safety controllers for interactive web services. We improve on the naIve runtime model to avoid state-space explosions and to increase the flow capacities of services.

A runtime system for interactive Web services

Interactive Web services are increasingly replacing traditional static Web pages. Producing Web services seems to require a tremendous amount of laborious low-level coding due to the primitive nature of CGI programming. We present ideas for an improved runtime system for interactive Web services built on top of CGI running on virtually every combination of browser and HTTP/CGI server. The runtime system has been implemented and used extensively in , a tool for producing interactive Web services.

A relational account of call-by-value sequentiality

We construct a model for FPC, a purely functional, sequential, call-by-value language. The model is built from partial continuous functions, in the style of Plotkin, further constrained to be uniform with respect to a class of logical relations. We prove that the model is fully abstract.

A Case Study on Using Automata in Control Synthesis

We study a method for synthesizing control programs. The method merges an existing control program with a control automaton. We have used monadic second order logic over strings to specify the control automata. Specifications are translated into automata by the Mona tool. This yields a new control program restricting the behavior of the old control program such that the specifications are satisfied. The method is presented through a concrete example.