The primary characteristic of an Ultra-Large-Scale (ULS) system is ultra-large size on any related dimension. A ULS system is generally considered as a system-of-systems with heterogeneous nodes and autonomous domains. As the size of a system-of-systems grows, and interoperability demand between sub-systems is increased, achieving more scalable and dynamic access control system becomes an important issue. The Attribute-Based Access Control (ABAC) model is a proper candidate to be used in such an access control system. The correct deployment and enforcement of ABAC policies in a ULS system requires secure and scalable collaboration among different distributed authorization components. A large number of these authorization components should be able to join different domains dynamically and communicate with each other anonymously. Dynamic configuration and reconfiguration of authorization components makes authorization system more complex to manage and maintain in a ULS system. In this paper, an access control middleware is proposed to overcome the complexity of deployment and enforcement of ABAC policies in ULS systems. The proposed middleware is data-centric and consists of two layers. The lower layer is a Data-Distribution-Service (DDS) middleware used for loosely-coupled-communication among authorization components. The upper layer is used for secure configuration and reconfiguration of authorization components. An executable model of the proposed middleware is also represented by a Colored-Petri-Net (CPN) model. This executable model is used to analyze the behavior of the proposed middleware.
 L. Northrop et al., "Ultra-Large-Scale Systems: The Software Challenge of the Future," Carnegie Mellon Software Engineering Institute, Ultra-Large-Scale Systems Study Report, 2006.
 D. Bell and L. LaPadula, "Secure computer system: Unified exposition and multics interpretation," Technical Report ESD-TR-75-306, The Mitre Corporation, March 1976.
 M. A. Harrison, W. L. Ruzzo, and J. D. Ullman, "Protection in Operating Systems," Communications of ACM, vol. 19, no. 8, pp. 461-471, ACM, 1976.
 D. Ferraiolo and R. Kuhn, "Role-Based Access Control," In Proceedings of 15th NIST-NCSC National Computer Security Conference, pp. 554-563, Baltimore, MD: ACM, 1992.
 R.S. Sandhu, E.J. Coyne, H.L. Feinstein and C.E.Youman, "Role-based Access Control Models," IEEE Computer, vol. 29, no. 2, pp. 38-47, IEEE 1996.
 A.R. Khan, "Access control in cloud computing Environment," ARPN Journal of Engineering and Applied Science, vol. 7, no. 5, pp. 613- 615, PK: ARPN, May 2012.
 B. Lang, I. Foster, F. Siebenlist, R. Ananthakrishnan, and T. Freeman, "Attribute based access control for grid computing," Math. Comput. Sci. (MCS) Div., Argonne Nat. Lab., Argonne, IL, Preprint ANL/MCS-P1367-0806, August 2006.
 T. Priebe, W. Dobmeier, and N. Kamprath, "Supporting Attribute-based Access Control in Authorization and Authentication Infrastructures with Ontologies," Journal of Software, vol. 2, no. 1, pp. 27-38, Academy Publisher, February 2007.
 S. Verma, S. Kumar, and M. Singh, "Comparative analysis of Role Base and Attribute Base Access Control Model in Semantic Web," International Journal of Computer Applications, vol. 46, no. 18, pp. 1-6, USA: FCS, May 2012.
 Feng Liang, Haoming Guo, Shengwei Yi, and Shi- long Ma, "A Multiple-Policy supported Attribute-Based Access Control Architecture within Large-scale Device Collaboration Systems," Journal of Networks, vol. 7, no. 3, pp. 524-531, Academy Publisher, March 2012.
 Tom Goovaerts, Lieven Desmet, and Wouter Joosen, "Scalable Authorization Middleware for Service Oriented Architectures," In Proceedings of the Third international conference on Engineering secure software and systems (ESSoS'11), February 2011, Springer-Verlag, pp. 221-233.
 S. Singh, K. Singh, and H. Kaur, "Design and Evaluation of Policy Based Authorization Model for large scale Distributed Systems," International Journal of Computer Science and Network Security (IJCSNS), vol. 9, no. 11, pp. 49-55. Nov. 2009.
 E. Damiani, S. De Capitani di Vimercati, and P. Samarati, "New Paradigms for Access Control in Open Environments," In Proceeding of 5th IEEE International Symposium on Signal Processing and Information, 2005, Greece: IEEE, pp. 540- 545.
 S. De Capitani di Vimercati, S. Foresti, S. Jajodia, and P. Samarati, "Access Control Policies and Languages," International Journal of Computational Science and Engineering (IJCSE), vol. 3, n. 2, pp. 94-102, Inderscience Publishers, 2007.
 Object Management Group (OMG), "Data Distribution Service for Real-Time Systems Specification," March 2004.
 R. Joshi, "Data oriented Architecture: A loosely Coupled Real time SOA," Real-Time Innovations, Inc., CA, Tech. Rep. Aug 2007.
 R. Joshi, "Data-Centric Invocable Services: A Core Design Pattern for Building Scalable Distributed Real-Time Systems," In Proceedings of the 2012 IEEE 15th International Symposium on Object/Component/Service-Oriented Real-Time Distributed Computing, Dec. 2012, IEEE Computer Society, pp. 1-7.
 Q. Wei, M. Ripeanu, and K. Beznosov, "Authorization Using the Publish-Subscribe Model," In Proceedings of IEEE International Symposium on Parallel and Distributed Processing with Applications (ISPA 2008), December 2008, NSW, IEEE, pp. 53-61.
 J. Bacon, K. Moody, and W. Yao, "Access control and trust in the use of widely distributed services," In Middleware 2001, Lecture Notes in Computer Science 2218, pp. 295-310, Springer, November 2001.
 J. Bacon, K. Moody, and W. Yao, "A Model of OASIS Role-Based Access Control and its Support for Active Security," ACM Transactions on Information and System Security (TISSEC), vol. 5, no. 4, pp. 492-540, USA: ACM, November 2002.
 L. I. Pesonen, D. M. Eyers, and J. Bacon, "Access control in decentralized publish/subscribe systems," Journal of Networks, vol. 2, no. 2, pp. 57-67, Academy Publisher, 2007.
 E. Yuan, J. Tong, "Attribute Based Access Control (ABAC) for Web Services," In Proceeding of IEEE Conference on Web Services (ICWS 2005), 2005, IEEE, pp. 561-569.
 A. Belokosztolszki, D. M. Eyers, P. R. Pietzuch, J. Bacon, and K. Moody, "Role-based access control for publish/subscribe middleware architectures," In Proceeding of international workshop on Distributed event-based systems, 2003, USA: ACM, pp. 1-8.
 J. Bacon, D. M. Eyers, J. Singh, and P. R. Pietzuch, "Access control in publish/subscribe systems," In Proceeding of 2nd International. Conference on Distributed event-based systems (DEBS), 2008, USA: ACM, pp. 23-34.
 J. Bacon, D. M. Eyers, K. Moody, and L. Pesonen, "Securing publish/subscribe for multi-domain systems," In Proceeding of 6th International Middleware Conference, vol. 3790, 2005, Springer, pp. 1- 20.
 N. Wang , D. Schmidt, H. Hag, and A. Corsaro, "Toward an adaptive data distribution service for dynamic large-scale network-centric operation and warfare (NCOW) systems," In Proceedings IEEE Military Communications (MILCOM'8), 2008, IEEE, pp. 1-7.
 Jose M. Lopez-Vega, Javier Povedano-Molina, Gerardo Pardo-Castellote, Juan M. Lpez-Soler, "A content-aware bridging service for publish/subscribe environments," Journal of Systems and Software, vol. 86, no.1, pp. 108-124, Elsevier, 2013.
 RTI, "Real-Time Innovations (RTI) DDS Data Distribution Service", http://www.rti.com/.
 Sung Yoon Chae, Sinae Ahn, Kyungran Kang, Jaehyuk Kim, Soohyung Lee, and Won-tae Kim, "Fast Discovery Scheme Using DHT-Like Overlay Network for a Large-Scale DDS," In Proceedings of FGIT-CA/CES3, 2011, Springer, pp. 128-137.
 Y.H. Long, Z.H. Tang, and X. Liu, "Attribute mapping for cross-domain access control," In Proceedings of Computer and Information Application (ICCIA), 2010, IEEE, pp. 343-347.
 OASIS. extensible access control markup language (xacml) version 3.0. Technical report, OASIS Standard, 2010.
 C. Ardagna, S. De Capitani di Vimercati, S. Paraboschi, E. Pedrini, P. Samarati, and M. Verdicchio, "Expressive and Deployable Access Control in Open Web Service Applications," IEEE Transactions on Service Computing (TSC), vol. 4, n. 2, pp. 96-109, IEEE, April-June 2011.
 P. Bonatti, S. De Capitani di Vimercati, and P. Samarati, "An Algebra for Composing Access Control Policies," ACM Transactions on Information and System Security (TISSEC), vol. 5, n. 1, pp. 1-35, ACM, February 2002.
 N. Li, Q. Wang, W. Qardaji, E. Bertino, P. Rao, J. Lobo, and D. Lin, "Access Control Policy Combining: Theory Meets Practice," In Proceeding of 14th ACM Symposium on Access Control Models and Technologies, 2009, ACM, pp. 135-144.
 W.M.P. van der Aalst and C. Stahl, Modeling Business Processes - A Petri Net-Oriented Approach, Cambridge, MA: MIT press, 2011.
 K. Jensen, L.M. Kristensen, and L. Wells, "Coloured Petri Nets and CPN Tools for Modeling and Validation of Concurrent Systems," International Journal on Software Tools for Technology Transfer (STTT), vol. 3, no. 4, pp. 213-254, Springer, 2007.
 CPN Tools, http://cpntools.org/.
 D.Fahland and C.Gierds, "Analyzing and Completing Middleware Designs for Enterprise Integration Using Coloured Petri Nets," In Proceedings of Conference on Advanced Information Systems Engineering (CAiSE 2013), 2013, Springer Berlin Heidelberg, pp. 400-416.
 L. Abidi, C. Crin, and S. Evangelista, "A Petri-Net Model for the Publish-Subscribe Paradigm and Its Application for the Verification of the BonjourGrid Middleware," In Proceedings of IEEE Services Computing (SCC), 2011, IEEE, pp. 496-503.
 "RTI Data Distribution Service", http://www.rti.com/products/dds/.