Protocol-Safe Workflow Support for Santa Claus

Practical software analysis techniques exploit a form a process description, mostly in some \ud avour of state diagram. Unlike typing information, these process structures are usually not passed down to the implementation level, and neither are they exploited in any form of consistency check. It is our belief that the information in most designs suffices to perform all sorts of consistency checks. This workshop paper studies a simple case where work\ud ow processes interact with `actual' objects at the implementation level, and demonstrates how useful protocol checking can be in making and keeping these processes consistent with each other

On Practical Verification of Processes

The integration of a formal process theory with a practically usable notation is not straightforward, but it is necessary for practical verification of process specifications. Given such an intermediate language, a verification process that gives useful feedback is not trivial either: Model checkers are not powerful enough to deal with object models, and theorem provers provide insu#cient feedback and are not certain to find a proof

Home-grown CASE tools with XML and XSLT

This paper demonstrates an approach to software generation where xml representations of models are transformed to implementations by XSLT style sheets. Although XSLT was not primarily intended for this use, it serves quite well. There are only few problems in this approach, and we identify these based on our examples

Extending Model Checking to Object Process Validation

Object-oriented techniques allow the gathering and modelling\ud of system requirements in terms of an application area. The\ud expression of data and process models at that level is a great\ud asset in communication with non-technical people in that area,\ud but it does not necessarily lead to consistent models. To avoid\ud that inconsistencies are only discovered during the latest phases\ud of development, it is helpful if analysis models can be verified,\ud especially if this is done in an automated process and if it gives\ud feedback that helps repair the models. This thesis presents\ud such an approach for the process aspects of analysis models

Protocol Assuring Universal Language

Conventionally, interfaces of objects export a set of messages with their types, and suggest nothing about the order in which these services may be accessed. This leaves room for a large number of runtime errors or misbehaviours in type correct designs. To mend this, we introduce the notion of protocol, expressing offered and expected orderings of messages, along with a notion of protocol correctness. We do this by defining the Protocol Assuring Universal Language Paul, which describes protocol aspects of classes, and a semantics of in terms of CSP

Suspected survivor bias in case–control studies: stratify on survival time and use a negative control

AbstractObjectivesSelection bias in case–control studies occurs when control selection is inappropriate. However, selection bias due to improper case sampling is less well recognized. We describe how to recognize survivor bias (i.e., selection on exposed cases) and illustrate this with an example study.Study Design and SettingA case–control study was used to analyze the effect of statins on major bleedings during treatment with vitamin K antagonists. A total of 110 patients who experienced such bleedings were included 18–1,018 days after the bleeding complication and matched to 220 controls.ResultsA protective association of major bleeding for exposure to statins (odds ratio [OR]: 0.56; 95% confidence interval: 0.29–1.08) was found, which did not become stronger after adjustment for confounding factors. These observations lead us to suspect survivor bias. To identify this bias, results were stratified on time between bleeding event and inclusion, and repeated for a negative control (an exposure not related to survival): blood group non-O. The ORs for exposure to statins increased gradually to 1.37 with shorter time between outcome and inclusion, whereas ORs for the negative control remained constant, confirming our hypothesis.ConclusionWe recommend the presented method to check for overoptimistic results, that is, survivor bias in case–control studies