\begin{thebibliography}{100} \bibitem{sA88} S.~Adams. \newblock An equivalence relation that is not freely generated. \newblock {\em Proc. Amer. Math. Soc.}, 102:565--566, 1988. \bibitem{wA41} W.~Ambrose. \newblock Representation of ergodic flows. \newblock {\em Ann. Math.}, 42:723--739, 1941. \bibitem{wA69} Wm. Arveson. \newblock Subalgebras of ${C}^*$-algebras. \newblock {\em Acta Math.}, 123:141--224, 1969. \bibitem{wA72} Wm. Arveson. \newblock Subalgebras of ${C}^*$-algebras. {II}. \newblock {\em Acta Math.}, 128:271--308, 1972. \bibitem{wA74} Wm. Arveson. \newblock Operator algebras and invariant subspaces. \newblock {\em Ann. Math.}, 100:433--532, 1974. \bibitem{wA76} Wm. Arveson. \newblock {\em An Invitation to ${C^*}$-Algebra}, volume~39 of {\em Graduate Texts in Mathematics}. \newblock Springer-Verlag, New York, 1976. \bibitem{ARp96} V.~Arzumanian and J.~Renault. \newblock Examples of pseudogroups and their ${C}^*$-algebras. \newblock To appear in the Proceedings of the Rome Conference on Operator Algebras, July 1996., 1996. \bibitem{AM66} L.~Auslander and C.~Moore. \newblock Unitary representations of solvable {L}ie groups. \newblock {\em Mem. Amer. Math. Soc.}, 62, 1966. \bibitem{bB86} B.~Blackadar. \newblock {\em {K}-{T}heory for {O}perator {A}lgebras}, volume~5 of {\em Mathematical Sciences Research Institute Publications}. \newblock Springer-Verlag, New York, 1986. \bibitem{eB96} E.~Blanchard. \newblock D\'{e}formations de ${C}^*$-alg\`{e}bres de {H}opf. \newblock {\em Bull. Soc. Math. France}, 124:141--215, 1996. \bibitem{dB95} D.~Blecher. \newblock A completely bounded characterization of operator algebras. \newblock {\em Math. Ann.}, 303:227--239, 1995. \bibitem{dB96} D.~Blecher. \newblock A generalization of {H}ilbert modules. \newblock {\em J. Functional Anal.}, 136:365--421, 1996. \bibitem{BMP97} D.~Blecher, P.~Muhly, and V.~Paulsen. \newblock Categories of operator modules ({M}orita equivalence and projective modules). \newblock {\em Mem. Amer. Math. Soc.}, 1997. \bibitem{BRS90} D.~Blecher, Z-J. Ruan, and A.~Sinclair. \newblock A characterization of operator algebras. \newblock {\em J. Functional Anal.}, 89:188--201, 1990. \bibitem{nB59/6/6} N.~Bourbaki. \newblock {\em Int\'egration}, volume 6, Chap. 6 of {\em \'Elements de Math\'ematique}. \newblock Hermann, Paris, 1959. \bibitem{nB66} N.~Bourbaki. \newblock {\em General Topology, {P}art 1}. \newblock Addison-Wesley, Reading, Mass., 1966. \bibitem{BGR77} L.~Brown, P.~Green, and M.~Rieffel. \newblock Stable isomorphisms and strong {M}orita equivalence of $c^*$-algebras. \newblock {\em Pacific J. Math.}, 71:349--363, 1977. \bibitem{rB87} R.~Brown. \newblock From groups to groupoids: a brief survey. \newblock {\em Bull. London Math. Soc.}, 19:113--134, 1987. \bibitem{rB88} R.~Brown. \newblock {\em Topology: A Geometric Account of General Topology, Homotopy Types and the Fundamental Groupoid}. \newblock Mathematics and its Applications. Ellis Horwood Limited, Chichester, 1988. \bibitem{fC84} F.~Combes. \newblock Crossed products and {M}orita equivalence. \newblock {\em Proc. London Math. Soc. (3)}, 49:289--306, 1984. \bibitem{aC79} A.~Connes. \newblock {\em Sur la th\'eorie non commutative de l`int\'egration}, volume 725 of {\em Lecture Notes in Mathematics}, pages 19--143. \newblock Springer-Verlag, Berlin, 1979. \bibitem{aC82} A.~Connes. \newblock {\em A survey of foliations and operator algebras}, volume~38 of {\em Proc. Sympos. Pure Math.}, pages 521--628. \newblock Amer. Math. Soc., Providence, 1982. \bibitem{aC94} A.~Connes. \newblock {\em Noncommutative Geometry}. \newblock Academic Press, Inc., San Diego, 1994. \bibitem{CT77} A.~Connes and M.~Takesaki. \newblock The flow of weights on factors of type {III}. \newblock {\em T\^{o}hoku Math. J.}, 29:473--575, 1977. \newblock Eratta. ibid. \textbf{30} (1978), 653--655. \bibitem{jC77} J.~Cuntz. \newblock Simple ${C}^*$-algebras generated by isometries. \newblock {\em Commun. Math. Phys.}, 57:173--185, 1977. \bibitem{CK80} J.~Cuntz and W.~Krieger. \newblock A class of ${C}^*$-algebras and topological {M}arkov chains. \newblock {\em Invent. Math.}, 56:251--268, 1980. \bibitem{CMW84} R.~Curto, P.~Muhly, and D.~Williams. \newblock Cross products of strongly {M}orita equivalent ${C}^*$-algebras. \newblock {\em Proc. Amer. Math. Soc.}, 90:528--530, 1984. \bibitem{kD88} K.~Davidson. \newblock {\em Nest Algebras}, volume 191 of {\em Pitman Research Notes in Mathematics}. \newblock Longman Scientific and Technical, Essex, 1988. \bibitem{kD95} K.~Davidson. \newblock When locally contractive representations are completely contractive. \newblock {\em J. Functional Anal.}, 128:186--225, 1995. \bibitem{DPP94} K.~Davidson, V.~Paulsen, and S.~Power. \newblock Tree algebras, semidiscreteness, and dilation theory. \newblock {\em Proc. London Math. Soc. (Series 3)}, 68:178--202, 1994. \bibitem{vDp96} V.~Deaconu. \newblock Embeddings of toral algebras and the corresponding {C}untz-{K}rieger algebras. \newblock Preprint, University of Nevada Reno, 1996. \bibitem{vD95a} V.~Deaconu. \newblock Groupoids associated with endomorphisms. \newblock {\em Trans. Amer. Math. Soc.}, 347:1779--1786, 1995. \bibitem{vD95b} V.~Deaconu. \newblock A path model for circle algebras. \newblock {\em J. Operator Theory}, 34:57--89, 1995. \bibitem{vD96} V.~Deaconu. \newblock Generalized {C}untz-{K}rieger algebras. \newblock {\em Proc. Amer. Math. Soc.}, 124:3427--3435, 1996. \bibitem{jD48} J.~Dieudonn\'{e}. \newblock Sur le th\'{e}or\`{e}me de {L}ebesgue-{N}ikodym. {III}. \newblock {\em Ann. Univ. Grenoble (N.S.)}, 23:25--53, 1948. \bibitem{jD77} J.~Dixmier. \newblock {\em ${C}^*$-Algebras}. \newblock Elsevier North-Holland, Inc., New York, 1977. \bibitem{jD81} J.~Dixmier. \newblock {\em {von} Neumann Algebras}. \newblock Elsevier North Holland, Inc., New York, 1981. \bibitem{DRS71} P.~Doubillet, G.~Rota, and R.~Stanley. \newblock On the foundations of combinatorial theory ({VI}): {T}he idea of a generating function. \newblock In {\em Proc. Sixth Berkeley Symposium in Math., Stat., and Prob., Vol. {II}}, pages 267--318, 1971. \bibitem{DP89} R.~Douglas and V.~Paulsen. \newblock {\em Hilbert Modules over Function Algebras}, volume 217 of {\em Pitman Research Notes in Mathematics Series}. \newblock Longman Scientific and Technical, Essex, 1989. \bibitem{hD59} H.~Dye. \newblock On groups of measure preserving transformations. {I}. \newblock {\em Amer. J. Math.}, 81:119--159, 1959. \bibitem{hD63} H.~Dye. \newblock On groups of measure preserving transformations. {II}. \newblock {\em Amer. J. Math.}, 85:551--576, 1963. \bibitem{eE66} E.~Effros. \newblock Global structure in von {N}eumann algebras. \newblock {\em Trans. Amer. Math. Soc.}, 121:434--454, 1966. \bibitem{eE86} E.~Effros. \newblock Advances in quantized functional analysis. \newblock In {\em Proc. ICM Berkeley}, 1986. \bibitem{EH67} E.~Effros and F.~Hahn. \newblock Locally compact transformation groups and ${C}^*$-algebras. \newblock {\em Memoirs Amer. Math. Soc.}, 75, 1967. \bibitem{FM43} H.~Federer and A.~Morse. \newblock Some properties of measurable functions. \newblock {\em Bull. Amer. Math. Soc.}, 49:270--277, 1943. \bibitem{FHM78} J.~Feldman, P.~Hahn, and C.~Moore. \newblock Orbit structure and countable sections for actions of continuous groups. \newblock {\em J. Functional Anal.}, 28:186--230, 1978. \bibitem{FM77a} J.~Feldman and C.~Moore. \newblock Ergodic equivalence relations, cohomology, and von {N}eumann algebras. {I}. \newblock {\em Trans. Amer. Math. Soc.}, 234:289--324, 1977. \bibitem{FM77b} J.~Feldman and C.~Moore. \newblock Ergodic equivalence relations, cohomology, and von {N}eumann algebras. {II}. \newblock {\em Trans. Amer. Math. Soc.}, 234:325--359, 1977. \bibitem{FD88a} J.~Fell and R.~Doran. \newblock {\em Representation of $*$-Algebras, Locally Compact Groups, and Banach $*$-Algebraic Bundles. Vol. 1}, volume 125 of {\em Pure and Applied Mathematics}. \newblock Academic Press, San Diego, 1988. \bibitem{FD88b} J.~Fell and R.~Doran. \newblock {\em Representation of $*$-Algebras, Locally Compact Groups, and Banach $*$-Algebraic Bundles. Vol. 2}, volume 126 of {\em Pure and Applied Mathematics}. \newblock Academic Press, Inc., San Diego, 1988. \bibitem{FF90} C.~Foia\c{s} and A.~Frazho. \newblock {\em The Commutant Lifting Approach to Interpolation Problems}, volume~44 of {\em Operator Theory: Advances and Applications}. \newblock Birkh\"{a}user, Basel-Boston-Berlin, 1990. \bibitem{pF74} P.~Forrest. \newblock Virtual subgroups of $\mathbb{R}^{n}$ and $\mathbb{Z}^{n}$. \newblock {\em Adv. in Math.}, 3:187--207, 1974. \bibitem{pG72} P.~Gabriel. \newblock Unzerlegbare darstellungen {I}. \newblock {\em Manuscr. Math.}, 6:71--103, 1972. \bibitem{pG92} P.~Gabriel. \newblock {\em Representations of Finite-Dimensional Algebras}, volume~73 of {\em Encyclopaedia of Mathematical Sciences}. \newblock Springer-Verlag, New York, 1992. \bibitem{plG94} P.-Y.~Le Gall. \newblock {\em Th\'eorie de {K}asparov \'equivariante et groupo\"ides}. \newblock PhD thesis, Universit\'e de {P}aris {VII}, June 1994. \bibitem{GR79} E.~Gootman and J.~Rosenberg. \newblock The structure of crossed product ${C}^*$-algebras: a proof of the generalized {E}ffros-{H}ahn conjecture. \newblock {\em Invent. Math.}, 52:283--298, 1979. \bibitem{pG77} P.~Green. \newblock $c^*$-algebras of transformation groups with smooth orbit space. \newblock {\em Pacific J. Math.}, 72:71--97, 1977. \bibitem{pG78} P.~Green. \newblock The local structure of twisted covariance algebras. \newblock {\em Acta mathematica}, 140:191--250, 1978. \bibitem{aH58} A.~Haefliger. \newblock Structures feuillet\'ees et cohomologie \`a valeur dans un faisceau de groupo\"ides. \newblock {\em Comm. Math. Helv.}, 32:248--329, 1958. \bibitem{aH84} A.~Haefliger. \newblock {\em Groupo\"ide d'holonomie et classifiant}, volume 116 of {\em Ast\'erisque}, pages 70--97. \newblock Soci\'et\'e {M}ath\'ematique de {F}rance, 1984. \bibitem{pH78a} P.~Hahn. \newblock Haar measure for measure groupoids. \newblock {\em Trans. Amer. Math. Soc.}, 242:1--33, 1978. \bibitem{pH78b} P.~Hahn. \newblock The regular representation of measure groupoids. \newblock {\em Trans. Amer. Math. Soc.}, 242:35--72, 1978. \bibitem{pH79} P.~Hahn. \newblock Reconstruction of a factor from measures on {T}akesaki's unitary equivalence relation. \newblock {\em J. Functional Anal.}, 31:263--271, 1979. \bibitem{pH41} P.~Halmos. \newblock The decomposition of measures. \newblock {\em Duke Math. J.}, 8:386--392, 1941. \bibitem{mH79} M.~Hamana. \newblock Injective envelopes of operator systems. \newblock {\em Publ. Res. Inst. Math. Sci., Kyoto Univ.}, 15:773--785, 1979. \bibitem{pH71} P.~Higgins. \newblock {\em Notes on Categories and Groupoids}, volume~32 of {\em Mathematical Studies}. \newblock Van Nostrand Reinhold Co., London, 1971. \bibitem{HS83} M.~Hilsum and G.~Skandalis. \newblock Stabilit\'e des $c^*$-alg\`ebres de feuilletages. \newblock {\em Ann. Inst. Fourier (Grenoble)}, 33:201--208, 1983. \bibitem{iK53} I.~Kaplansky. \newblock Modules over operator algebras. \newblock {\em Trans. Amer. Math. Soc.}, 75:839--858, 1953. \bibitem{gK80} G.~Kasparov. \newblock Hilbert ${C}^*$-modules: {T}heorems of {S}tinespring and {V}oiculescu. \newblock {\em J. Operator Theory}, 4:133--150, 1980. \bibitem{dK82} D.~Kastler. \newblock Connes' noncommutative integration theory. \newblock {\em Commun. Math. Phys.}, 85:99--120, 1982. \bibitem{aK83} A.~Kumjian. \newblock {\em Diagonals in algebras of continuous trace}, volume 1132 of {\em Lecture Notes in Mathematics}, pages 297--311. \newblock Springer-Verlag, New York, 1983. \bibitem{aK84} A.~Kumjian. \newblock On localizations and simple ${C}^*$-algebras. \newblock {\em Pacific J. Math.}, 112:141--192, 1984. \bibitem{aK86} A.~Kumjian. \newblock On ${C}^*$-diagonals. \newblock {\em Canad. J. Math.}, 38:969--1008, 1986. \bibitem{aK88} A.~Kumjian. \newblock On equivariant sheaf cohomology and elementary ${C}^*$-bundles. \newblock {\em J. Operator Theory}, 20:207--240, 1988. \bibitem{KMRWp96} A.~Kumjian, P.~Muhly, J.~Renault, and D.~Williams. \newblock The {B}rauer group of a locally compact groupoid. \newblock Preprint, January 1997. \bibitem{KPRp96} A.~Kumjian, D.~Pask, and I.~Raeburn. \newblock Cuntz-{K}rieger algebras of directed graphs. \newblock Preprint, October 1996. \bibitem{KPRR97} A.~Kumjian, D.~Pask, I.~Raeburn, and J.~Renault. \newblock Graphs, groupoids, and {C}untz-{K}rieger algebras. \newblock {\em J. Functional Anal.}, 1997. \bibitem{KRW96} A.~Kumjian, I.~Raeburn, and D.~Williams. \newblock The equivariant {B}rauer groups of commuting free and proper actions are isomorphic. \newblock {\em Proc. Amer. Math. Soc.}, 124:809--817, 1996. \bibitem{cK33} K.~Kuratowski. \newblock {\em Topology}. \newblock Academic Press, New York and London, 1966. \newblock English translation, revised and augmented, of the fourth French edition. \bibitem{eL94} E.~C. Lance. \newblock {\em Hilbert ${C}^*$-modules: A toolkit for operator algebraists}, volume 124 of {\em London Mathematical Society Lecture Note Series}. \newblock Cambridge University Press, Cambridge, 1994. \bibitem{kM87} K.~Mackenzie. \newblock {\em Lie Groupoids and Lie Algebroids in Differential Geometry}, volume 124 of {\em London Mathematical Society Lecture Note Series}. \newblock Cambridge University Press, Cambridge, 1987. \bibitem{gM49} G.~Mackey. \newblock Imprimitivity for representations of locally compact groups. {I}. \newblock {\em Proc. Nat. Acad. Sci. U.S.A.}, 35:537--545, 1949. \bibitem{gM52} G.~Mackey. \newblock Induced representations of groups. {I}. \newblock {\em Ann. Math.}, 55:101--139, 1952. \bibitem{gM53} G.~Mackey. \newblock Induced representations of locally compact groups. {II}, the {F}robenius reciprocity theorem. \newblock {\em Ann. Math.}, 58:193--220, 1953. \bibitem{gM57} G.~Mackey. \newblock Borel structures in groups and their duals. \newblock {\em Trans. Amer. Math. Soc.}, 85:134--165, 1957. \bibitem{gM58} G.~Mackey. \newblock Unitary representations of group extensions {I}. \newblock {\em Acta Math.}, 99:265--311, 1958. \bibitem{gM62} G.~Mackey. \newblock Point realizations of transformation groups. \newblock {\em Illinois J. Math.}, 6:327--335, 1962. \bibitem{gM63b} G.~Mackey. \newblock Ergodic theory, group theory, and differential geometry. \newblock {\em Proc. Nat. Acad. Sci. U.S.A.}, 50:1184--1191, 1963. \bibitem{gM63a} G.~Mackey. \newblock Infinite dimensional group representations. \newblock {\em Bull. Amer. Math. Soc.}, 69:628--686, 1963. \bibitem{gM63c} G.~Mackey. \newblock {\em Mathematical Foundations of Quantum Mechanics}. \newblock The Mathematical Physics Monograph Series. W. A. Benjamin, Inc., New York, 1963. \bibitem{gM66} G.~Mackey. \newblock Ergodic theory and virtual groups. \newblock {\em Math. Ann.}, 166:187--207, 1966. \bibitem{gM74} G.~Mackey. \newblock Ergodic theory and its significance for statistical mechanics and probability theory. \newblock {\em Adv. in Math.}, 12:178--268, 1974. \bibitem{gM76} G.~Mackey. \newblock {\em The Theory of Unitary Group Representations}. \newblock Chicago Lectures in Mathematics Series. The University of Chicago Press, Chicago, 1976. \newblock An expanded version of notes on lectures given at the University of Chicago in 1955, and circulated in mimeographed form under the title: "The Theory of Group Representations". \bibitem{tM84a} T.~Masuda. \newblock Groupoid dynamical systems and crossed product, {I}-{T}he case of ${W}^*$-systems. \newblock {\em Publ. Res. Inst. Math. Sci., Kyoto Univ.}, 20:929--957, 1984. \bibitem{tM84b} T.~Masuda. \newblock Groupoid dynamical systems and crossed products, {II}: the case of ${C}^*$-systems. \newblock {\em Publ. Res. Inst. Math. Sci., Kyoto Univ.}, 20:959--970, 1984. \bibitem{rM93} R.~Mercer. \newblock The full group of a countable measurable equivalence relation. \newblock {\em Proc. Amer. Math. Soc.}, 117:323--333, 1993. \bibitem{cM76a} C.~Moore. \newblock Group extensions and cohomology for locally compact groups. {III}. \newblock {\em Trans. Amer. Math. Soc.}, 221:1--33, 1976. \bibitem{cM76b} C.~Moore. \newblock Group extensions and cohomology for locally compact groups. {IV}. \newblock {\em Trans. Amer. Math. Soc.}, 221:34--58, 1976. \bibitem{MS88} C.~Moore and C.~Schochet. \newblock {\em Global Analysis on Foliated Spaces}, volume~9 of {\em Mathematical Sciences Research Institute Publications}. \newblock Springer-Verlag, New York, 1988. \bibitem{kM58} K.~Morita. \newblock Duality of modules and its applications to the theory of rings with minimum condition. \newblock {\em Sci. Rep. Tokyo Kyoiku Daigaku, Sect. A}, 6:85--142, 1958. \bibitem{MQS91} P.~Muhly, C.~Qiu, and B.~Solel. \newblock Coordinates, nuclearity, and spectral subspaces in operator algebras. \newblock {\em J. Operator Theory}, 26:313--332, 1991. \bibitem{MRW87} P.~Muhly, J.~Renault, and D.~Williams. \newblock Equivalence and isomorphism for groupoid ${C}^{*}$-algebras. \newblock {\em J. Operator Theory}, 17:3--22, 1987. \bibitem{MW90} P.~Muhly and D.~Williams. \newblock Continuous trace groupoid ${C}^*$-algebras. \newblock {\em Math. Scand.}, 66:231--241, 1990. \bibitem{MW92} P.~Muhly and D.~Williams. \newblock Continuous trace groupoid ${C}^*$-algebras. {II}. \newblock {\em Math. Scand.}, 70:127--145, 1992. \bibitem{MW95} P.~Muhly and D.~Williams. \newblock Groupoid cohomology and the {D}ixmier-{D}ouady class. \newblock {\em Proc. London Math. Soc. (3)}, 71:109--134, 1995. \bibitem{jvN32} J.~{v}on Neumann. \newblock Zur {O}peratorenmethode in der klassischen {M}echanik. \newblock {\em Ann. Math.}, 33:789--791, 1932. \bibitem{kP67} K.~Parthasarathy. \newblock {\em Probability Measures on Metric Spaces}. \newblock Academic Press, New York, 1967. \bibitem{wP73} W.~Paschke. \newblock Inner product modules over $b^*$-algebras. \newblock {\em Trans. Amer. Math. Soc.}, 182:443--468, 1973. \bibitem{aPp96} A.~Paterson. \newblock Groupoids, inverse semigroups, and their operator algebras. \newblock Unpublished book manuscript, 1996. \bibitem{gP79} G.~Pedersen. \newblock {\em $C^*$-algebras and their Automorphism Groups}. \newblock Academic Press, London, 1979. \bibitem{iP96a} I.~Putnam. \newblock ${C}^*$-algebras from {S}male spaces. \newblock {\em Can. J. Math.}, 48:175--195, 1996. \bibitem{iP96} I.~Putnam. \newblock Hyperbolic systems and generalized {C}untz-{K}rieger algebras. \newblock Lecture notes from the Summer School in Operator Algebras, Odense, Denmark, 1996. \bibitem{iR81} I.~Raeburn. \newblock On the {P}icard group of a continuous-trace ${C}^*$-algebra. \newblock {\em Trans. Amer. Math. Soc.}, 263:183--205, 1981. \bibitem{RR88} I.~Raeburn and J.~Rosenberg. \newblock Crossed products of continuous-trace ${C}^*$-algebras. \newblock {\em Trans. Amer. Math. Soc.}, 305:1--45, 1988. \bibitem{RT85} I.~Raeburn and J.~Taylor. \newblock Continuous-trace ${C}^*$-algebras with given {D}ixmier-{D}ouady class. \newblock {\em J. Austral. Math. Soc. (Series A)}, 38:394--407, 1985. \bibitem{RW85} I.~Raeburn and D.~Williams. \newblock Pull-backs of ${C}^*$-algebras and crossed products by certain diagonal actions. \newblock {\em Trans. Amer. Math. Soc.}, 287:755--777, 1985. \bibitem{RW93} I.~Raeburn and D.~Williams. \newblock Dixmier-{D}ouady classes of dynamical systems and crossed products. \newblock {\em Canad. J. Math.}, 45:1032--1066, 1993. \bibitem{RW98} I.~Raeburn and D.~Williams. \newblock {\em Morita Equivalence and Continuous Trace ${C}^*$-algebras}. \newblock AMS Surveys and Monographs. Amer. Math. Soc., Providence, 1998. \bibitem{aR71} A.~Ramsay. \newblock Virtual groups and group actions. \newblock {\em Adv. in Math.}, 6:253--322, 1971. \bibitem{aR74} A.~Ramsay. \newblock Boolean duals of virtual groups. \newblock {\em J. Functional Anal.}, 15:56--101, 1974. \bibitem{aR76} A.~Ramsay. \newblock Nontransitive quasiorbits in {M}ackey's analysis of group extensions. \newblock {\em Acta Math.}, 137:17--48, 1976. \bibitem{aR82} A.~Ramsay. \newblock Topologies for measured groupoids. \newblock {\em J. Functional Anal.}, 47:314--343, 1982. \bibitem{RS81} M.~Reed and B.~Simon. \newblock {\em Methods of Modern Mathematical Physics {I}. Functional Analysis}. \newblock Academic Press, San Diego, 1981. \newblock 2nd Printing. \bibitem{bR83} B.~Reinhart. \newblock {\em Differential Geometry of Foliations}, volume~99 of {\em Ergebnisse der Mathematik und ihrer Grenzgebiete}. \newblock Springer-Verlag, 1983. \bibitem{jR80} J.~Renault. \newblock {\em A Groupoid Approach to $C^{*}$-Algebras}, volume 793 of {\em Lecture Notes in Mathematics}. \newblock Springer-Verlag, New York-Heidelberg, 1980. \bibitem{jR82} J.~Renault. \newblock {\em ${C}^*$-algebras of groupoids and foliations}, volume~38 of {\em Proc. Sympos. Pure Math.}, pages 339--350. \newblock Amer. Math. Soc., Providence, 1982. \bibitem{jR83} J.~Renault. \newblock {\em Two applications of the dual groupoid of a ${C}^*$-algebra}, volume 1132 of {\em Lecture Notes in Mathematics}, pages 434--445. \newblock Springer-Verlag, New York, 1983. \bibitem{jR87} J.~Renault. \newblock Repr\'{e}sentation des produits crois\'{e}s d'alg\`{e}bres de groupo\"{i}des. \newblock {\em J. Operator Theory}, 18:67--97, 1987. \bibitem{jR91} J.~Renault. \newblock The ideal structure of groupoid crossed product ${C}^*$-algebras. \newblock {\em J. Operator Theory}, 25:3--36, 1991. \bibitem{mR74} M.~Rieffel. \newblock Induced representations of ${C}^*$-algebras. \newblock {\em Adv. Math.}, 13:176--257, 1974. \bibitem{mR82} M.~Rieffel. \newblock {\em Applications of strong {M}orita equivalence to transformation group ${C}^*$-algebras}, volume~38 of {\em Proc. Sympos. Pure Math.}, pages 299--310. \newblock Amer. Math. Soc., 1982. \bibitem{vR52} V.~Rohlin. \newblock On the fundamental ideas of measure theory. \newblock {\em Amer. Math. Soc. Transl.}, 71:55pp, 1952. \bibitem{aS86} A.~Seda. \newblock On the continuity of {H}aar measure on topological groupoids. \newblock {\em Proc. Amer. Math. Soc.}, 96:115--120, 1986. \bibitem{aW96} A.~Weinstein. \newblock Groupoids: {U}nifying internal and external symmetry. \newblock {\em Notices of the Amer. Math. Soc.}, 43:744--752, 1996. \bibitem{jW67a} J.~Westman. \newblock Locally trivial ${C}^r$ groupoids and their representations. \newblock {\em Pacific J. Math.}, 20:339--349, 1967. \bibitem{jW67} J.~Westman. \newblock Nontransitive groupoid algebras. \newblock Unpublished preprint from the University of California, Irvine, 1967. \bibitem{jWp71} J.~Westman. \newblock Groupoid theory in algebra, topology, and analysis. \newblock Unpublished preprint from the University of California at Irvine., 1971. \bibitem{rZ84} R.~Zimmer. \newblock {\em Ergodic Theory and Semisimple Groups}. \newblock Birkh\"{a}user, Boston, 1984. \end{thebibliography}