Gustaf Neumann

A scenario-driven role engineering process for functional RBAC roles

In this paper we present a novel scenario-driven role engineering process for RBAC roles. The scenario concept is of central significance for the presented approach. Due to the strong human factor in role engineering scenarios are a good means to drive the process. We use scenarios to derive permissions and to define tasks. Our approach considers changeability issues and enables the straightforward incorporation of changes into affected models. Finally we discuss the experiences we gained by applying the scenario-driven role engineering process in three case studies.

A discourse on complexity of process models

Complexity has undesirable effects on, among others, the correctness, maintainability, and understandability of business process models. Yet, measuring complexity of business process models is a rather new area of research with only a small number of contributions. In this paper, we survey findings from neighboring disciplines on how complexity can be measured. In particular, we gather insight from software engineering, cognitive science, and graph theory, and discuss in how far analogous metrics can be defined on business process models.

Detection and prediction of errors in EPCs of the SAP reference model

Up to now there is neither data available on how many errors can be expected in process model collections, nor is it understood why errors are introduced. In this article, we provide empirical evidence for these questions based on the SAP reference model. This model collection contains about 600 process models expressed as Event-driven Process Chains (EPCs). We translated these EPCs into YAWL models, and analyzed them using the verification tool WofYAWL. We discovered that at least 34 of these EPCs contain errors. Moreover, we used logistic regression to show that complexity of EPCs has a significant impact on error probability.

An integrated approach to engineer and enforce context constraints in RBAC environments

We present an approach that uses special purpose role-based access control (RBAC) constraints to base certain access control decisions on context information. In our approach a context constraint is defined as a dynamic RBAC constraint that checks the actual values of one or more contextual attributes for predefined conditions. If these conditions are satisfied, the corresponding access request can be permitted. Accordingly, a conditional permission is an RBAC permission that is constrained by one or more context constraints. We present an engineering process for context constraints that is based on goal-oriented requirements engineering techniques, and describe how we extended the design and implementation of an existing RBAC service to enable the enforcement of context constraints. With our approach we aim to preserve the advantages of RBAC and offer an additional means for the definition and enforcement of fine-grained context-dependent access control policies.

Understanding the occurrence of errors in process models based on metrics

Business process models play an important role for the management, design, and improvement of process organizations and process-aware information systems. Despite the extensive application of process modeling in practice, there are hardly empirical results available on quality aspects of process models. This paper aims to advance the understanding of this matter by analyzing the connection between formal errors (such as deadlocks) and a set of metrics that capture various structural and behavioral aspects of a process model. In particular, we discuss the theoretical connection between errors and metrics, and provide a comprehensive validation based on an extensive sample of EPC process models from practice. Furthermore, we investigate the capability of the metrics to predict errors in a second independent sample of models. The high explanatory power of the metrics has considerable consequences for the design of future modeling guidelines and modeling tools.

An approach to engineer and enforce context constraints in an RBAC environment

This paper presents an approach that uses special purpose RBAC constraints to base certain access control decisions on context information. In our approach a context constraint is defined as a dynamic RBAC constraint that checks the actual values of one or more contextual attributes for predefined conditions. If these conditions are satisfied, the corresponding access request can be permitted. Accordingly, a conditional permission is an RBAC permission which is constrained by one or more context constraints. We present an engineering process for context constraints, that is based on goal-oriented requirements engineering techniques, and describe how we extended the design and implementation of an existing RBAC service to enable the enforcement of context constraints. With our approach we aim to preserve the advantages of RBAC, and offer an additional means for the definition and enforcement of fine-grained context-dependent access control policies.

Faulty EPCs in the SAP reference model

Little is known about error probability in enterprise models as they are usually kept private. The SAP reference model is a publically available model that contains more than 600 non-trivial process models expressed in terms of Event-driven Process Chains (EPCs). We have automatically translated these EPCs into YAWL models and analyzed these models using WofYAWL, a verification tool based on Petri nets, in order to acquire knowledge about errors in large enterprise models. We discovered that at least 34 of these EPCs contain errors (i.e., at least 5.6% is flawed) and analyzed which parts of the SAP reference model contain most errors. This systematic analysis of the SAP reference model illustrates the need for verification tools such as WofYAWL.

An approach to extract RBAC models from BPEL4WS processes

The Business Process Execution Language for Web services (BPEL) has become the defacto standard for Web service composition. Yet, it does not address security aspects. This paper is concerned with access control for BPEL based processes. We present an approach to integrate role-based access control (RBAC) and BPEL on the meta-model level. Moreover, we show that such integration can be used to automate steps of the role engineering process. In particular, we extract RBAC models from BPEL processes and present an XSLT converter that transforms BPEL code to the XML import format of the xoRBAC software component.

From a Social Wiki to a Social Workflow System

This paper presents an approach for using wikis in an organizational context and a proto-type implementation for developing a wiki-based workflow system. We provide general considerations and requirements for changing a wiki’s application context from public to organizational and will describe consequences for wiki architecture and policy management. The presented workflow system is based on an open-source wiki tool and is targeted at collaborative workflow design and activity management.

Design and implementation of a flexible RBAC-service in an object-oriented scripting language

In this paper we present the design and implementation of the xorbac component that provides a flexible RBAC service. The xorbac, implementation conforms to level 4a of the unified NIST model for RBAC and can be reused for arbitrary applications on Unix or Windows with a C or Tcl linkage. xorbac runtime elements can be serialized and recreated from RDF data models conforming to a well-defined RDF schema. Furthermore we present our experiences with xorbac for the deployment within the HTTP environment for a web-based mobile code system.