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ACM"],"published-print":{"date-parts":[[2008,2]]},"abstract":"<jats:p>XrML is becoming a popular language in industry for writing software licenses. The semantics for XrML is implicitly given by an algorithm that determines if a permission follows from a set of licenses. We focus on a fragment of the language and use it to highlight some problematic aspects of the algorithm. We then correct the problems, introduce formal semantics, and show that our semantics captures the (corrected) algorithm. Next, we consider the complexity of determining if a permission is implied by a set of XrML licenses. We prove that the general problem is undecidable, but it is polynomial-time computable for an expressive fragment of the language. We extend XrML to capture a wider range of licenses by adding negation to the language. Finally, we discuss the key differences between XrML and MPEG-21, an international standard based on XrML.<\/jats:p>","DOI":"10.1145\/1326554.1326558","type":"journal-article","created":{"date-parts":[[2008,2,28]],"date-time":"2008-02-28T14:02:33Z","timestamp":1204207353000},"page":"1-42","update-policy":"https:\/\/doi.org\/10.1145\/crossmark-policy","source":"Crossref","is-referenced-by-count":12,"title":["A formal foundation for XrML"],"prefix":"10.1145","volume":"55","author":[{"given":"Joseph Y.","family":"Halpern","sequence":"first","affiliation":[{"name":"Cornell University, Ithaca, New York"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Vicky","family":"Weissman","sequence":"additional","affiliation":[{"name":"Cornell University, Ithaca, New York"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"320","published-online":{"date-parts":[[2008,2,22]]},"reference":[{"key":"e_1_2_1_1_1","doi-asserted-by":"publisher","DOI":"10.5555\/1009380.1009672"},{"key":"e_1_2_1_2_1","unstructured":"ContentGuard. 2001. XrML: The digital rights language for trusted content and services. Available at http:\/\/www.xrml.org\/.  ContentGuard. 2001. XrML: The digital rights language for trusted content and services. Available at http:\/\/www.xrml.org\/."},{"key":"e_1_2_1_3_1","doi-asserted-by":"publisher","DOI":"10.5555\/829514.830540"},{"key":"e_1_2_1_4_1","doi-asserted-by":"crossref","unstructured":"Ellison C. Frantz B. Lampson B. Rivest R. Thomas B. and Ylonen T. 1999a. SPKI certificate theory. Available at http:\/\/www.ietf.org\/html.charters\/spki-charter.html. Internet RFC 2693.   Ellison C. Frantz B. Lampson B. Rivest R. Thomas B. and Ylonen T. 1999a. SPKI certificate theory. Available at http:\/\/www.ietf.org\/html.charters\/spki-charter.html. Internet RFC 2693.","DOI":"10.17487\/rfc2693"},{"key":"e_1_2_1_5_1","unstructured":"Ellison C. Frantz B. Lampson B. Rivest R. Thomas B. and Ylonen T. 1999b. Simple public key certificate. Available at http:\/\/world.std.com\/~cme\/spki.txt. Internet RFC 2693.  Ellison C. Frantz B. Lampson B. Rivest R. Thomas B. and Ylonen T. 1999b. Simple public key certificate. Available at http:\/\/world.std.com\/~cme\/spki.txt. Internet RFC 2693."},{"key":"e_1_2_1_6_1","doi-asserted-by":"publisher","DOI":"10.5555\/959088.959093"},{"volume-title":"Proceedings of the 16th IEEE Computer Security Foundations Workshop. IEEE Computer Society Press","author":"Halpern J. Y.","key":"e_1_2_1_7_1"},{"key":"e_1_2_1_8_1","doi-asserted-by":"publisher","DOI":"10.5555\/1009380.1009679"},{"volume-title":"ODRL: The open digital rights language initiative.","year":"2001","author":"Iannella R.","key":"e_1_2_1_9_1"},{"volume-title":"Proceedings of the 1997 IEEE Symposium on Security and Privacy. IEEE Computer Society Press","author":"Jajodia S.","key":"e_1_2_1_10_1"},{"key":"e_1_2_1_11_1","doi-asserted-by":"publisher","DOI":"10.5555\/882495.884431"},{"key":"e_1_2_1_12_1","doi-asserted-by":"publisher","DOI":"10.1145\/605434.605438"},{"key":"e_1_2_1_13_1","doi-asserted-by":"publisher","DOI":"10.1007\/s10207-005-0073-0"},{"volume-title":"Proceedings of the 2002 IEEE Symposium on Security and Privacy. IEEE Computer Society Press","author":"Li N.","key":"e_1_2_1_14_1"},{"volume-title":"XACML: The extensible access control markup language, version 2.0.","year":"2005","author":"Moses T.","key":"e_1_2_1_15_1"},{"key":"e_1_2_1_16_1","unstructured":"MPEG. 2004. Information technology---Multimedia framework (MPEG-21)---Part 5: Rights expression language (ISO\/IEC 21000-5:2004). Available at http:\/\/www.iso.ch\/iso\/en\/.  MPEG. 2004. Information technology---Multimedia framework (MPEG-21)---Part 5: Rights expression language (ISO\/IEC 21000-5:2004). Available at http:\/\/www.iso.ch\/iso\/en\/."},{"key":"e_1_2_1_17_1","doi-asserted-by":"crossref","unstructured":"Nerode A. and Shore R. 1997. Logic for Applications 2nd ed. Springer-Verlag New York.   Nerode A. and Shore R. 1997. Logic for Applications 2nd ed. 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