Articles

Michael Mey, Managing Consultant at Obvious Works, holds a diploma in Computer Science from Furtwangen University, Germany, where he first explored AI and neural networks. With extensive experience in international software projects, particularly in the financial industry, Michael has held key roles at major corporations and launched a crypto startup through an incubation program, blending corporate and entrepreneurial insights. An Agile coach and trainer, he specializes in Requirements Engineering and AI integration. Michael is engaged in the IREB Special Interest Group AI and regularly speaks at conferences like REConf, REFSQ, and Scrum Day. As co-creator of the AIxRE Masterclass, he is dedicated to helping organizations optimize their processes by integrating AI into Requirements Engineering practices.

• AI Assistants in Requirements Engineering | Part 1

Prof. Dr. Salinesi is an active academic who teaches topics in relation with software design such as Requirements Engineering, and Software Product Lines. He was involved in many funded research projects (FP4, FP5, H2020, ANR) and was the leader for collaborations and consultancy works for various companies such as France Télécom, SNCF, Renault, EDF or REXEL). He has been General Chair of SPLC, CAiSE, REFSQ international conferences, and was Organizing Chair of the 13th IEEE International Conference on Requirements Engineering.

At IREB, Prof Salinesi has acted for 2 mandates as Second Chair of the Executive Committee. He is now Full Member, member of the Editorial Board, and WG Member.

• Conversation with an Artificial Intelligence

Howard Podeswa is a thought leader in the intersection of agile and business analysis. For over twenty years, he has been helping large organizations optimize their analysis and planning practices for agile software development approaches. He has authored a number of books that have become staple references for practitioners, most recently: The Agile Guide to Business Analysis and Planning: From Strategic Plan to Continuous Value Delivery - How Product Owners and Business Analysts (BAs) maximize the value of the product developed by the team, by integrating BA competencies with agile methodologies (Addison-Wesley Professional; 1st edition, 2021). Other works include UML for the IT Business Analyst (2009), and The Business Analyst’s Handbook (2008).

At Noble Inc., he has provided agile and business analysis services to clients worldwide, including the International Standards Organization (ISO), Moody’s, the Mayo Clinic, TELUS, TD Bank, LabCorp, the U.S. Food and Drug Administration (FDA), Mawer Investment Management Ltd., Bell Nexia, and REI Coop. He is currently advising IIBA on its Nimble initiative.

To contact Howard for in-house and public training and coaching services, please email howardpodeswa@nobleinc.ca or find him on LinkedIn @howardpodeswa

• Why Your Agile Organization Needs a High-Performing Requirements Engineering Competency
• The Business Case for Agile Business Analysis
• Five Questions

For more than twenty years, Rainer Grau has accompanied companies on their way enterprise agility. He supports companies in their efforts to continuously develop and create sustainable value for customers and employees. For him, it is particularly exciting to find out which methods, techniques and approaches are suitable for scaling agility and building the right product and the right service for the customer. Business analysis and requirements engineering are two essential disciplines in this context, which also generate high value in an agile setup - even if perhaps lived completely differently compared to a classic project approach.

Rainer's background of experience in business agility is based on his consulting work with companies from various industries. Stages of his professional life include Distinguished Consultant and Partner at Zühlke Engineering, Head of Business Development at digitec Galaxus, responsible for courses at universities of applied sciences on the topic of agility, founder of the Swiss Agile Leaders Circle, founder of Denkplan Verein and active involvement in communities around agility, business analysis and requirements engineering.

If there is still time left, Rainer Grau likes to spend it with his family, doing sports, playing his guitar and reading novels.

• Mission Possible
• Innovation Arena

Gil Regev has been a researcher at EPFL since 1997 in the fields of enterprise information systems, requirements engineering, change management and knowledge management. Since 2008 he is also manager and consultant at Itecor, a boutique consultancy firm. Previously Gil developed software for computer peripherals at Logitech, in Switzerland and California.

• A General Systems Thinking Perspective on the CPRE

Alain Wegmann is a full professor at the School of Computer and Communication Sciences, EPFL, Switzerland. He worked 14 years for Logitech (Switzerland, Taiwan, US) in positions ranging from software developer, IS manager, manufacturing engineering to VP of engineering and OEM marketing before joining the EPFL in 1997. His teaching, consulting and research are in the fields of enterprise architecture, requirements engineering and service engineering.

• A General Systems Thinking Perspective on the CPRE

Olivier Hayard has been a consultant and in charge of IT and Knowledge Management at Itecor, a boutique consultancy firm, since 1993. Olivier’s main interests are business analysis and requirements management, as practitioner, trainer and researcher.

• A General Systems Thinking Perspective on the CPRE

Till-J. Faßold is Expert Strategic Planning at 1&1, Germany. In this role – besides other responsibilities – he coaches professionals from various departments and is responsible for the requirements engineering processes. Till-J. Faßold hold a master’s degree in information management from the University of Koblenz and is certified to the IREB CPRE Expert Level.

• Requirements Engineering and Domain Knowledge

Freelance trainer and consultant in Software Engineering. 20 years of work experience, including 7 years as consultant and project manager, 10 years in research and university teaching, and two guest professorships. Associate member at IREB, co-author of syllabus and handbook for the CPRE Advanced Level in Requirements Management. www.herrmann-ehrlich.de

• Requirements Engineering in Job Offers

Maya Daneva, PhD, is Senior Member of Scientific Staff in the Services and Cybersecurity group at the University of Twente, the Netherlands. Her research interests are requirements engineering for large systems, security requirements engineering, requirements-based project estimation, user feedback analytics, and empirical research methods. Maya has a strong international exposure having spent two years of her career in Germany at the University of Saarbruecken and in the IDS Scheer, and 9 years as a business process analyst for SAP Enterprise Recourse Planning projects at TELUS Corporation, Canada’s second largest telecommunication company.

• Requirements Engineering in Job Offers

Chong Wang is an assistant professor at Wuhan University. She has over 10 years of work experience in research and university teaching. Her research interests include requirements engineering, software engineering, and service computing.

• Requirements Engineering in Job Offers

Nelly Condori-Fernandez is an assistant professor at the Universidade da Coruna (Spain) and research associate of the Vrije Universiteit Amsterdam (The Netherlands). Her research focuses on topics related to quality requirements prioritization and sustainability. She has published 85 articles in indexed journals and ranked conferences. Besides, she has been involved in several European projects.

• Requirements Engineering in Job Offers

Luisa Mich is an Associate Professor of Computer Science at the University of Trento, Italy. Her research interests include requirements engineering, creativity and web strategies. She is an author of more than 150 papers.
 

• Interview with John Mylopoulos
• Requirements Elicitation (ReqElic) in My Company

Daniel Méndez is an Associate Professor for Software Engineering at the Blekinge Institute of Technology, Sweden and Senior Scientist at fortiss, the research institute of the Free State of Bavaria for software-intensive systems and services. His research is on Empirical Software Engineering with a particular focus on interdisciplinary, qualitative research in Requirements Engineering and its quality improvement. He regularly publishes in various software engineering publications and has occupied several key positions in venues of the empirical software engineering community. He is a member of the ACM, the IEEE Computer Society, and the German association of university professors and lecturers, and he serves as the representative to ISERN, the International Empirical Software Engineering Research Network. Further information is provided at www.mendezfe.org.

• What is the Relevance of Requirements Engineering Research to Practitioners?
• Modeling Requirements and Context as a means for Automated Requirements Validation

Xavier Franch is Professor at the Universitat Politècnica de Barcelona (UPC-BarcelonaTech), Spain. He is Council Member and Full Member of the IREB association. He has published over 200 peer-reviewed papers in conferences and journals, many of them related to requirements engineering. He was Program Co-Chair of the RE’16 and REFSQ’11 conferences, and he belongs to the Editorial Board of the Requirements Engineering Journal (Springer) and Information Software and Technology (IST) journals, among others. He is coordinator of the Q-Rapids project and participates in the OpenReq project, both in the H2020 programme. He organizes workshops concerning requirements engineering for NLP4RE, CrowdRE, JIT-RE and others.

• What is the Relevance of Requirements Engineering Research to Practitioners?
• Modeling Requirements and Context as a means for Automated Requirements Validation

Andreas Vogelsang is a post-doc researcher in the software & systems engineering group at the Technical University of Munich. He works on model-based requirements engineering and participated in several research collaborations with industrial partners especially from the automotive industry. His research published was published in relevant international conferences like RE, REFSQ, or ICSE.

• What is the Relevance of Requirements Engineering Research to Practitioners?
• Modeling Requirements and Context as a means for Automated Requirements Validation

Rana Siadati is currently a PhD student in Software Requirements Engineering and also a visiting lecturer by the School of Computer Science at the University of Hertfordshire. Alongside these roles, Rana has many years of academic and industrial experience, also at managerial level, gained in the UK and abroad.

• Learning from history: The case of Software Requirements Engineering

Paul Wernick is a Senior Lecturer in Computer Science at the University of Hertfordshire. Dr Wernick has taken leading roles in the ProSim series of software process simulation workshops, and the IEEE Workshop on Software Evolvability. Dr Wernick’s current research interests cover the high-level human environment within which software processes occur and their simulation, and computer security.

• Learning from history: The case of Software Requirements Engineering

Vito Veneziano is a Senior Lecturer in Computer Science at the University of Hertfordshire, and his interests range from software engineering, HCI, requirements analysis and system modelling, to how software systems impact on organisations. Previously Dr Veneziano worked in IT and project management, business application development, software design and consultancy.

• Learning from history: The case of Software Requirements Engineering

Grigory Grin is a Chief Software Architect at Axinom – software supplier for Media- and In-Flight Entertainment solutions based in Germany and Estonia.
Grigory studied mathematics and graduated from the Ural State University in Russia in 1995. During his 25 years career on the software development field, Grigory had responsibilities in a broad range of roles – Development, Architecture, Business Analysis, Project Management. His main strengths are in alignment between the customer needs and contractors technical capabilities and solution portfolio to deliver the highest business value.
As a practitioner, Grigory has successfully led multiple multi-million euro projects for world-known brands in the aerospace industry with significant challenges on the field of Requirements Engineering.

• When the rubber hits the road

Jason Hansen obtained a BS in Chemical Engineering from Michigan Tech. He left the work force in 2005 to focus on raising an adopted special needs daughter. In 2015, he decided to return to school and obtained his AAAS in Network Admin. He is working as a tutor at GRCC while pursuing a Master’s Degree in Computer Software Engineering at GVSU.

• Challenges in the elicitation and determination of precise requirements from animal stakeholders

Hans van Loenhoud MSc is a consultant and teacher at Taraxacum in the Netherlands. He has been working in software development for more than 35 years, starting as a Cobol programmer and later on specialized in test and quality management.
In this role, he has been teaching various ISTQB test courses and has been chair of TestNet, the Dutch association of professional software testers. In recent years, he joined IREB to build a bridge between software testing and requirements engineering. He gives various Business Analysis, Requirements Engineering and Software Testing trainings. Hans is also a lecturer at the Amsterdam University of Applied Sciences for these topics and participates in the IREB advanced level Elicitation working group.

• On the right track
• The goal is to solve the problem
• Translating Exam Questions

Thijmen works as IT architect at Kommuninvest acting as technical lead for its digitalization initiative and growing CI/CD and Agile practice in the company. His work on the mini-QAW started in his role as researcher at ABB, where he worked on software architectures with colleagues around the globe. He authored publications at leading international software conferences, receiving two best paper awards. Thijmen graduated cum-laude in software engineering from VU University in the Netherlands and Malardalen University in Sweden.

• Discover Quality Requirements with the Mini-QAW

Michael Keeling is a software engineer at LendingHome and the author of Design It! From Programmer to Software Architect. In his career so far, he has worked on a variety of interesting software systems including IBM Watson, enterprise search applications, financial platforms, and Navy combat systems. Michael has a master’s degree in software engineering from Carnegie Mellon University and a bachelor’s degree in computer science from the College of William and Mary. Contact him via Twitter @michaelkeeling or his website, https://www.neverletdown.net

• Discover Quality Requirements with the Mini-QAW

Will Chaparro is a software development manager in IBM’s Watson Group. He spent over 5 years designing and building complex enterprise search solutions as a managing consultant. Prior to IBM he spent 11 years as a software engineer. He has a BS in Computer Science from the University of Pittsburgh.

• Discover Quality Requirements with the Mini-QAW

Inge Kress is a specialist in psychosomatic medicine. Currently she works at the University Hospital of Erlangen/Germany. Her research and clinical work focuses on stress and emotion processing. Besides practicing medicine, she engages in medical education regarding psychosomatic issues, giving scientific lectures and workshops. Her main objective is to learn and teach about cognitive, emotional and physiological processes and their impact on mental and physical health, especially in work life.

• To Brainstorm or Not to Brainstorm

As a Requirements Engineering Consultant and Trainer with SOPHIST GmbH, Anja Schwarz supports clients of different fields in all requirements engineering aspects. As a trainer, she prepares her participants for the CPRE Foundation Level certification as well as for the CPRE Advanced Level Elicitation & Consolidation certification. She also supports the IREB e.V. as Lead of the Elicitation and Consolidation working group. The elicitation of innovative requirements and thus the requirements for creativity have always fascinated her, leading to the cooperation with Inge Kress. Together, they brought the neurological aspects of creativity into the context of requirements engineering, also resulting in this article.


• To Brainstorm or Not to Brainstorm

Fabrício Laguna is the first CBAP © in Latin America (CBAP - Certified Professional in Business Analysis by IIBA © - International Institute of Business Analysis), also certified PMP Project Manager by PMI.

He holds a degree in Computer Science from USP, an MBA in Business Administration from FUNDACE (Foundation linked to FEA USP) and a degree in Entrepreneurship from the EMPRETEC program at SEBRAE.

He is currently President of the IIBA São Paulo Chapter, where he coordinated the translation project of Guia BABOK © into the Portuguese language. He was a reviewer of the 3rd version of this guide in partnership with specialists in Business Analysis from several countries.

He has experience in systems development and in the implementation of systems development methodologies in several companies, mainly in the financial market.
Parallel to his work in the IT area, he participated in several theater groups as an actor and playwright. The mixture of technical and communication skills has created a singular facility to act as an instructor in training and lectures, which has been recognized by all the places where it operates.

He has been teaching for more than 15 years, having undergraduate courses (Federal University of São Carlos), post-graduation (University of Marília, IBPI SP and RJ and Anhembi Morumbi), extension courses (USP and UNAERP), and more than 10,000 hours of training for professionals in several large companies.

• REQM guidance matrix

Manon Penning has a broad background in the fields of IT and education. She is an educational specialist, requirements engineer, quality analyst and trainer currently employed by Improve Quality Services, a provider of consultancy and training. Via Improve Quality Services she has been working for several Dutch companies over the past few years.

• Biased Toddlers
• The Genius Toddler Challenge

Manon Penning has a broad background in the fields of IT and education. She is an educational specialist, requirements engineer, quality analyst and trainer currently employed by Improve Quality Services, a provider of consultancy and training. Via Improve Quality Services she has been working for several Dutch companies over the past few years.

• Biased Toddlers
• The Genius Toddler Challenge

SOPHIST-in-chief (formally: founder and executive partner of the SOPHIST GmbH), chief consultant, coach and trainer. Looking back over 25 years of professional experience, a lot has come up: a company, 6 books, 55 employees, countless articles and presentations and a whole lot of experience. My passion for project consultation might account for the fact that, until now, I do not “only” manage, but I am still directly involved in projects and close to customers.
 

• Stable? Fragile? Agile! Attractive but reasonable

Human capital is not merely a phrase we do not live, it is one of the most important goods we have. With regards to my function as a Project coordinator, my aspiration is to target the optimized commitment of the individualized abilities, strengths and talents of the SOPHISTs. In addition, I am permanently looking for new employees for the team, taking care of our trainees, development of the staff and thus I am constantly supporting our executives. I benefit from my studies of Social Sciences, my multi-year experience in Human Resources and my sense for the positive.

• Stable? Fragile? Agile! Attractive but reasonable

Christoph Wolf works for more than 15 years as Requirements Engineer, Business Analyst, Project Manager and Quality Assurance Manager. He has built up a Business Analysis team and led it for several years. Since last year, he is consultant at SwissQ and supports clients in requirements engineering and quality assurance with focus on delivering business value. 

• The Business Analysis Center of Excellence

After studying physics in Germany and New Zealand, Gunnar Harde worked as software engineer, later as IT consultant and project manager for IT and business consultancies and research institutes. Since 2007 he is responsible for the development of several IT systems of the Group Quality Assurance at Volkswagen and shapes the cooperation between IT and business department strategically and methodically. Harde is Certified Scrum Product Owner and expert in agile management.

• Managing the Invisible
• Agility and Obligation
• Agility and Obligation

Sven is senior consultant|trainer at inspearit|cibit academy. He has worked on aligning business and IT at various organisations for more than 20 years. Both at profit and non-profit organisations Sven has helped teams and individuals to reach improvements in processes and results. He masters and applies several methods and techniques. Sven has helped many persons to achieve more with the right use of requirements engineering techniques and with agile ideas and frameworks. He loves to share his experience with others.

• Requirements Engineering and Agile

Ina Paschen is a Senior Business Analyst and Project Manager at Zühlke Schweiz. As a practitioner and consultant she helps ensure her clients deliver successful projects: a clear project set-up, a solid requirements engineering process, clear requirements and business processes to be developed, an improved development process or a transparent communication between development and management to build trust, to reduce impediments, and therefore bridging worlds like agile and non-agile.

• Bridging communication gaps with a Feature Tree

Emmerich Fuchs has more than 30 years of experience in application development and is a consultant in business process modelling, requirements engineering and quality assurance. Since 1985 he has been teaching at technical colleges and universities of applied science, and is a well-known trainer, as well as a co-author and an examinant, as well as an active member of IREB.

• Bridging communication gaps with a Feature Tree

After studying physics in Germany and New Zealand, Gunnar Harde worked as software engineer, later as IT consultant and project manager for IT and business consultancies and research institutes. Since 2007 he is responsible for the development of several IT systems of the Group Quality Assurance at Volkswagen and shapes the cooperation between IT and business department strategically and methodically. Harde is Certified Scrum Product Owner and expert in agile management.

• Managing the Invisible
• Agility and Obligation
• Agility and Obligation

Ellen Gottesdiener is an internationally recognized leader in the convergence of agile + requirements + product management + project management. Ellen is founder and principal of EBG Consulting, which helps organizations adapt how they collaborate to improve business outcomes.

Ellen’s passion is helping people use modern product requirements practices to build valued products and great teams. She provides training, coaching, and facilitates discovery and planning workshops across diverse industries, including education, energy, financial services, pharmaceutical, software, transportation, and telecommunications.

Ellen is a world-renowned writer, speaker, and presenter. Her most recent book, co-authored with Mary Gorman, is Discover to Deliver: Agile Product Planning and Analysis. Ellen is author of two other acclaimed books: Requirements by Collaboration and The Software Requirements Memory Jogger.

You can connect digitally with Ellen via her Blog | Twitter | Newsletter | LinkedIn 

• Agile Product Ownership

Ulf Ackermann currently works as a Requirements Engineer in the B2B Industry Commerce division of T-Systems Multimedia Solutions GmbH. His degree in commercial information technology at the Dresden University of Applied Sciences helps him to capture customer requirements from both business and technical perspectives. He has more than 7 years’ experience in large scale E-Commerce projects and specializes in the area of project procedure models. He states: “Structuring a project from the few known variables to produce an appealing offering for the customer is the most challenging and in the end rewarding part of my daily work.”

• Customized Agile RE Process

Dirk Fritsch is a Principal Consultant in the requirements division at QA Systems GmbH.  He has over 10 years of experience in business analysis, process modelling and requirements engineering and has worked on customer projects from every sector. He collaborated in research projects at the University of Duisburg/Essen and the University of Leipzig, addressing recurring issues from customer projects to improve existing methods using new technologies and solutions. In his current work he focuses on training and coaching for requirements management using classical and agile methods.

• Customized Agile RE Process

Gareth is an experienced business analyst and product owner who has been working in the telecoms and other industries for longer than he’d like to be specific about. He has been an active member of IREB for some years and is a co-author and examiner within the RE@Agile working group. He lives and works in Germany having successfully escaped from a small, slightly uncooperative island.

• Splitting Requirements at Scale
• RE in Agile Projects: Survey Results
• RE in Agile Projects: a Survey
• How agile can Requirements Engineers really be?

Alexander Rachmann advises companies on the linking business and IT. His strong interdisciplinary knowledge of business administration and computer science enables him to work as an ideal Requirements Engineer, Business Analyst, or System Analyst. He has worked in industries such as e-commerce, healthcare, IT security, and software development. He holds a doctorate degree in economics, master's degrees in computer science and information science and a diploma in business computer science.

• Product Owner in Scrum

Jesko Schneider worked as a consultant with a focus on Business Analysis, Requirements Management and Usability Engineering. He built up consulting services for Requirements Engineering and Usability Engineering in an international consulting company. His industry focus lies on telecommunications. He is a well-known trainer for Certified Professional for Requirements Engineering from the IREB. In his role as Requirements Engineer, Business Analyst, System Analyst or Product Owner, he is always the linkage between business and IT. He holds a degree in media informatics.

• Product Owner in Scrum

Frank Engel looks back on over 10 years’ experience in project management and Requirements Engineering. Prior to his time as a Partner of the Anforderungsfabrik, he was responsible for an international consulting company as Unit Manager. Topic of his business unit was Requirements Engineering and Management. His role in projects is Product Owner, Project Manager and Requirements Engineer. He studied business information systems. Always linking business and IT!

• Product Owner in Scrum

Founder of the consulting company “Crescendo Technologies”, Joseph Aracic is a System Engineering Consultant, focusing on requirements management techniques and processes, product line engineering and model driven engineering.

Prior to this, Joseph has been the manager of the Telelogic (Now an IBM Rational brand) French Professional Services team for requirements management and architecture modeling. Joseph has been involved in various system engineering projects (mainly in the defense industry) as consultant/coach in system engineering techniques deployment.

• A key technique

Cristina Palomares is a PhD student in the Software Engineering for Information Systems Research Group (GESSI) at the Universitat Politècnica de Catalunya (UPC). Her PhD thesis deals about the construction, use and evolution of software requirement patterns for the reuse of requirements knoledge.

She has published several papers and presented posters and demos in requirements engineering conferences like in IEEE International Requirements Engineering Conference (RE) and the International Working Conference on Requirements Engineering: Foundation for Software Quality (REFSQ). She is the coordinator of developers of the PABRE System for supporting requirements reuse.

• What is the Relevance of Requirements Engineering Research to Practitioners?
• Requirements Reuse

Dr. Carme Quer is associate professor in the Service and Information System Engineering department (ESSI) at the Universitat Politècnica de Catalunya (UPC). She is member of the Software Engineering for Information Systems Research Group (GESSI) at the UPC. Her main research lines are requirements engineering and software quality.

She has published several papers in requirements engineering conferences like in the IEEE International Requirements Engineering Conference (RE) and the International Working Conference on Requirements Engineering: Foundation for Software Quality (REFSQ). She was General Chair of the Workshop on Requirements Engineering (WER) held in 2008.

• What is the Relevance of Requirements Engineering Research to Practitioners?
• Requirements Reuse

Xavier Franch is Professor at the Universitat Politècnica de Barcelona (UPC-BarcelonaTech), Spain. He is Council Member and Full Member of the IREB association. He has published over 200 peer-reviewed papers in conferences and journals, many of them related to requirements engineering. He was Program Co-Chair of the RE’16 and REFSQ’11 conferences, and he belongs to the Editorial Board of the Requirements Engineering Journal (Springer) and Information Software and Technology (IST) journals, among others. He is coordinator of the Q-Rapids project and participates in the OpenReq project, both in the H2020 programme. He organizes workshops concerning requirements engineering for NLP4RE, CrowdRE, JIT-RE and others.

• What is the Relevance of Requirements Engineering Research to Practitioners?
• Requirements Reuse

For more than twenty years, Rainer Grau has accompanied companies on their way enterprise agility. He supports companies in their efforts to continuously develop and create sustainable value for customers and employees. For him, it is particularly exciting to find out which methods, techniques and approaches are suitable for scaling agility and building the right product and the right service for the customer. Business analysis and requirements engineering are two essential disciplines in this context, which also generate high value in an agile setup - even if perhaps lived completely differently compared to a classic project approach.

Rainer's background of experience in business agility is based on his consulting work with companies from various industries. Stages of his professional life include Distinguished Consultant and Partner at Zühlke Engineering, Head of Business Development at digitec Galaxus, responsible for courses at universities of applied sciences on the topic of agility, founder of the Swiss Agile Leaders Circle, founder of Denkplan Verein and active involvement in communities around agility, business analysis and requirements engineering.

If there is still time left, Rainer Grau likes to spend it with his family, doing sports, playing his guitar and reading novels.

• Mission Possible
• Innovation Arena