Abstract
In the relational model of data, Rissanen's Theorem provides the basis for the usual normalization process based on decomposition of relations. However, many difficulties occur if information is incomplete in databases and nulls are required to represent missing or unknown data. We concentrate here on the notion of outer join and find some reasonable conditions to guarantee that outer join will also preserve the lossless join property for two relations. Next we provide a generalization of this result to several relations.
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Paolo Atzeni and Nicola M. Morfuni,Functional dependencies in relations with null values, Information Processing Letters, vol. 18, pp. 233–238, 1984.
Paolo Atzeni and Nicola M. Morfuni,Functional dependencies and constraints on null values in database relations, Information and Control, vol. 70, no. 1, pp. 1–31, July 1986.
C. Beeri, R. Fagin, D. Maier, and M. Yannakakis,On the desirability of acyclic database schemes, Jour. of ACM, vol. 30, no. 3, pp. 479–513, 1983.
E. F. Codd,Extending the database relational model to capture more meaning, ACM Trans. on Database Systems, vol. 4, no. 4, pp. 397–434, 1979.
C. J. Date,An Introduction to Database Systems, Volume II, Addison-Wesley, Reading, 1983.
R. Fagin,Multivalued dependencies and a new normal form for relational databases, ACM Trans. on Database Systems, vol. 2, no. 3, pp. 262–278, 1977.
R. Fagin, A. O. Mendelzon, and J. D. Ullman,A simplified universal relation assumption and its properties, ACM Trans. Database Systems, vol. 7, no. 3, pp. 343–360, 1982.
R. Fagin,Degrees of acyclicity for hypergraphs and relational database schemes, Jour. of ACM, vol. 30, no. 3, pp. 514–550, 1983.
I. J. Heath, IBM internal memo, April, 1971.
Sushil Jajodia and Frederick Neal Springsteel,Construction of universal instances for loop-free network databases using a join-like operation, IEEE Trans. on Software Engineering, vol. SE-13, no. 7, pp. 811–819, July 1987.
M. LaCroix and C. Pirotte,Generalized joins, ACM SIGMOD Record, vol. 8, no. 3, pp. 14–15, 1976.
Y. E. Lien,On the equivalence of database models, Jour. of ACM, vol. 29, no. 2, pp. 333–362, 1982.
Y. E. Lien,Multivalued dependencies with null values, Proc. Int. Conf. on Very Large Data Bases, pp. 61–66, 1979.
J. Rissanen,Independent component of relations, ACM Trans. Database Systems, vol. 2, no. 4, pp. 317–325, 1977.
Jeffrey D. Ullman,Principles of Database Systems, Second Edition, Computer Science Press, Rockville, Maryland, 1982.
Carlo Zaniolo,Database relations with null values, Jour. of Computer and System Sciences, vol. 1984, pp. 142–166, 1984.
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Jajodia, S., Springsteel, F.N. Lossless outer joins with incomplete information. BIT 30, 34–41 (1990). https://doi.org/10.1007/BF01932129
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DOI: https://doi.org/10.1007/BF01932129