Regular Paper Experience from Introducing Unified Modeling Language/Systems Modeling Language at Saab Aerosystems Henric Andersson,1, * Erik Herzog,1 Gert Johansson,2 and Olof Johansson3 1Saab Aerosystems AB, Brödern Ugglas gata, SE-581 88 Linköping, Sweden 2Combitech AB, SE-580 15 Linköping, Sweden 3Linköping University, Linköping, Sweden INTRODUCING UML/SysML AT SAAB AEROSYSTEMS Received 17 September 2008; Revised 23 February 2009; Accepted 31 August 2009, after one or more revisions Published online 9 November 2009 in Wiley Online Library (wileyonlinelibrary.com) DOI 10.1002/sys.20156 ABSTRACT A Unified Modeling Language/Systems Modeling Language (UML/SysML) subset was the modeling notation selected for an aerospace systems engineering project at Saab Aerosystems. In this paper, the rationale for selecting UML/SysML is given, along with a description of the situation at the project planning stage regarding business conditions, method and tools support. The usage of use case, sequence, and activity diagrams are described as well as definition of functional chains with SysML. Furthermore, the connections to system implementation activities including code generation and simulation are discussed. The advantages and disadvantages of using UML/SysML from experience in an industrial context are reported. It is also described how UML/SysML is related to industrial research projects in the Model Based Systems Engineering (MBSE) methods and tools area. Introducing UML/SysML with a methodology and a supporting toolset in an operative organization require a clear strategy, including planning, just-in-time training, and mentor support. Finally, industrial needs for further development of SysML are discussed. © 2009 Wiley Periodicals, Inc. Syst Eng 13: 369–380, 2010 Key words: Systems Modeling Language; Unified Modeling Language; model based systems engineering; unmanned aerial vehicle 1. INTRODUCTION considerable focus on Model Based System Engineering (MBSE) (also referred to as Model Based System Develop- Unambiguous specification and design has long been the ment) as the vehicle for managing complexity and improving objective in the development of complex heterogeneous sys- specification clarity and consistency [see Oliver, Kelliher, and tems. Multiple methods and languages have been proposed in Keegan, 1997; Alford et al., 1992; Lykins, Friedenthal, and the literature and evaluated in industry, as reported in Stevens Meilich, 2000; Wymore, 2002; Long and Baker, 1996]. et al. [1998] and Mar [1991]. In recent years there has been The acronym MBSE has been used in many different contexts with slightly different meanings. For a control engi- neer, MBSE might refer to model based specification of, for *Author to whom all correspondence should be addressed (henric.anders- example, controllers in tools like Matlab/Simulink. For a [email protected]; [email protected]). software engineer, MBSE might involve modeling of soft- Systems Engineering Vol 13, No. 4, 2010 ware in UML. In fact, modeling has become a standard and © 2009 Wiley Periodicals, Inc. an accepted method for the design activity in several engineer- 369 370 ANDERSSON ET AL. ing domains. This is in contrast to Systems Engineering (SE) The rest of this paper is outlined as follows: Section 2 of complex heterogeneous systems where, until recently, sys- presents the pilot project for MBSE introduction, the Skeldar tem modeling was the exception rather than the rule. This has UAV system. Section 3 presents the palette of improvement now changed with the introduction of languages such as initiatives underway at Saab Aerosystems and, further; the UML2 and in particular SysML. See, for example, OMG rationale for selecting UML/SysML for systems modeling is [2006]. Still there are few publications describing experience presented in Section 4. Sections 5 and 6 present the method gained from introducing systems modeling in large projects. selected for introducing MBSE and experience gained from This paper presents the approach taken and lessons learned the introduction. Section 7 outlines desirable extensions and when introducing systems modeling (from now on referred to modifications to SysML to provide better support to systems as MBSE) using UML/SysML at Saab Aerosystems. The engineers, and a summary with conclusions is presented in company develops and produces aircraft systems, and its main Section 8. product is the JAS 39 Gripen lightweight fighter aircraft. Traditionally, the company has a history of few large pro- grams, tightly coupled to a single customer— the Swedish Air 2. UAV DEMONSTRATORS AND PRODUCTS Force. The commercial environment for Saab Aerosystems is now changing in several ways: Saab has limited previous experience of UAV systems and has consequently conducted a series of studies to gain a better • New product development and production programs understanding of the challenges associated with the develop- with shorter turnarounds are being introduced, such as ment and operation of autonomous air vehicles. The studies the UAV program (Unmanned Aerial Vehicle) described conducted include two flying demonstrators prior to the first in this paper. product—Skeldar. A brief overview of the demonstrators and the Skeldar product is presented below. • The Gripen program is expanding into a multicustomer, export environment which is forcing Saab to improve its handling of product variants and upgrade programs 2.1. UAV Demonstrators for older configurations. SHARC (Swedish Highly Advanced Research Configura- • Customers expect Saab to identify, fund, and develop tion) technology demonstrator is used to develop and new capabilities rather than the traditional customer- demonstrate autonomous behavior. paid development model. FILUR (Flying Innovative Low-observable Unmanned • Market desire to contract for complete systems instead Research vehicle) is a stealth demonstrator to demon- of parts, for example, delivering integrated solutions strate the effect of signature management. rather than providing aircrafts and support equipment under separate contracts. Both SHARC and FILUR were developed using Saab’s experience of model based design gained from fighter devel- As a consequence of the changes identified above, there is opment, partly described in Andersson and Sundqvist [2006]. a drive to improve engineering productivity and quality, and the introduction of MBSE is considered to have high poten- 2.2. The Skeldar UAV Product tial. This paper reports on experience gained from introducing MBSE and UML/SysML on the Skeldar autonomous helicop- SKELDAR V150 is Saab’s first UAV product—a short to ter system. Even if, in a strict sense, a UML2 subset was used medium range mobile UAV system that makes it possible to for modeling, the results are considered applicable for perform take-off and landings without field preparations or SysML, as the chosen subset and supporting methods align extra equipment, and which is suitable for both military and well with SysML projects. civil applications. Figure 1 presents the aerial vehicle and Figure 1. The Skeldar air vehicle and a possible ground station layout. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.] Systems Engineering DOI 10.1002/sys INTRODUCING UML/SysML AT SAAB AEROSYSTEMS 371 ground control station. The modular design allows different the EMPIRE project, a set of systems engineering tech- configurations such as alternative UAV Control System niques/tools were introduced along with supporting processes (UCS) deployment, different ground-segment solutions and and methods. Further change initiatives in the SE area have to choose among payloads: been conducted, establishing the prerequisites for continuing engineering support and process improvements. Examples Aerial Vehicle Avionics. Avionics include redundant com- puters, Global Positioning System (GPS) receivers, are: Inertial Measurement Units (IMUs), an air-data sys- • tem, and a magnetic heading indicator allowing fully Graphical modeling and code generation with System- Build by National Instruments [2007] autonomous operation. • UAV Control System (UCS). The UCS is also a modular- Software Configuration and Change Management with Dimensions by Serena [2007] ized solution, according to NATO standard STANAG • 4586 [NATO, 2004], and can be integrated onto differ- Requirements Management with DOORS by Telelogic ent hardware platforms such as trailers or containers. [2007a] • Incorporating air vehicle and sensor operator worksta- Software Modeling with UML and Rhapsody by tions, the UCS is capable of simultaneously controlling Telelogic [2007b] more than one UAV. • Product Data Management with Teamcenter by Sie- Data Links and Payloads. Communication between the mens [2008]. air vehicle and the UCS is achieved via secure direct The ongoing methods and tools change program at Saab links containing sensor and command/control data Aerosystems is called MBSE, and it integrates a range of which are transmitted via separate communication change initiatives. As a means to analyze strengths and weak- links. The air vehicle is designed to carry a range of nesses of different modeling methods and to organize the payloads such as Electro optical/Infrared (EO/IR), work in the change program, the modeling tools and related Synthetic Aperture Radar (SAR), and Electronic War- techniques/methods was divided and sorted into modeling fare (EW) sensors. domains, as shown in Figure 2. One purpose was to verify that the efforts were broad enough