Foundations of fast communication via XML

Communication with XML often involves pre-agreed document types. In this paper, we propose an offline parser generation approach to enhance online processing performance for documents con-forming to a given DTD. Our examination of DTDs and the languages they define demonstrates the existence of ambiguities. We present an algorithm that maps DTDs to deterministic context-free grammars defining the same languages. We prove the grammars to be LL(1) and LALR(1), making them suitable for standard parser generators. Our experiments show the superior performance of generated optimized parsers. Our results generalize from DTDs to XML Schema specifications with certain restrictions, most notably the absence of namespaces, which exceed the scope of context-free grammars

BOOST -- A Satellite Mission to Test Lorentz Invariance Using High-Performance Optical Frequency References

BOOST (BOOst Symmetry Test) is a proposed satellite mission to search for violations of Lorentz invariance by comparing two optical frequency references. One is based on a long-term stable optical resonator and the other on a hyperfine transition in molecular iodine. This mission will allow to determine several parameters of the standard model extension in the electron sector up to two orders of magnitude better than with the current best experiments. Here, we will give an overview of the mission, the science case and the payload.Comment: 11 pages, 2 figures, accepted for publication in Phys. Rev.

On the Construction of Correct Compiler Back-Ends: An ASM-Approach

Existing works on the construction of correct compilers have at least one of the following drawbacks: (i) correct compilers do not compile into machine code of existing processors. Instead they compile into programs of an abstract machine which ignores limitations and properties of real-life processors. (ii) the code generated by correct compilers is orders of magnitudes slower than the code generated by unverified compilers. (iii) the considered source language is much less complex than real-life programming languages. This paper focuses on the construction of correct compiler backends which generate machine-code for real-life processors from realistic intermediate languages. Our main results are the following: (i) We present a proof approach based on abstract state machines for bottom-up rewriting system specifications (BURS) for back-end generators. A significant part of this proof can be parametrized with the intermediate and machine language. (ii) The performance of the code constructed by our approach is in the same order of magnitude as the code generated by non-optimizing unverified C-compilers

Mechanized Verification of Compiler Backends

We describe an approach to mechanically prove the correctness of BURS specifications and show how such a tool can be connected with BURS based back-end generators [9]. The proofs are based on the operational semantics of both source and target system languages specified by means of Abstract State Machines [15]. In [31] we decomposed the correctness condition based on these operational semantics into local correctness conditions for each BURS rule and showed that these local correctness conditions can be proven independently. The specification and verification system PVS is used to mechanicalyy verify BURS-rules based on formal representations of the languages involved. In particular, we have defined PVS proof strategies which enable an automatic verification of the rules. Using PVS, several erroneous rules have been found. Moreover, from failed proof attempts we were able to correct them. 1 Introduction There exist a variety of techniques to construct efficient code produci..