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Enabling Semantic Access to Enterprise RDB Data Jun YUAN David H. JONES Mathematics & Computing Technology Boeing Phantom Works BOEING is a trademark of Boeing Management Company. Copyright © 2007 Boeing. All rights reserved. Motivation Boeing Technology | Phantom Works Semantic Mappings Semantic Query Generator Information consumer E&IT | Mathematics and Computing Technology • Advanced knowledge about database technology is needed to query a DB. • • • Semantic Query Translator • Post-Query Processing What if a database schema changes? • Query Interface • Database • Schema 1.0 Schema 2.0 Schema 1.1 Schema 2.1 Schema N Copyright © 2007 Boeing. All rights reserved. • Understanding schemata. Knowing query language syntax. … Many changes are not driven by semantics. – – – – – Normalization or De-normalization. Using different DBMS products. Change of data types. Stored procedures vs. Views. … Query statements usually have to be modified accordingly. About query answers • • • A table of rows. Ever-growing information sharing. Is retrieved information semantically understandable? What can we do better? Semantic Query Layer Boeing Technology | Phantom Works Semantic Mappings Semantic Query Generator Information consumer Semantic Query Translator Post-Query Processing Query Interface Database Schema 1.0 Schema 2.0 Schema 1.1 Schema 2.1 Schema N Copyright © 2007 Boeing. All rights reserved. E&IT | Mathematics and Computing Technology • Semantic Independence. • Isolate semantics from the underlying nonsemantics things in DB technology. • Present information consumer with the semantic part only. • Benefits • Semantics of data is explicitly presented by ontology. • Query against ontology directly. • Semantics of query answers is explicitly presented by ontology. • Non-semantic changes are hidden from end users. • … Semantics Models in Database Technology Boeing Technology | Phantom Works E&IT | Mathematics and Computing Technology • Semantic model is commonly used in DB design. • Three-level DB design • Conceptual level model (ER Diagram) is a kind of semantic model. • When and why explicit semantics gets embedded? • • • • From conceptual model to logical model. Schema normalization. No explicit relationships. … • Explicit semantic representation was there, but disappeared later in the process. • Schema re-engineering is a practice to recover such explicit semantics. Copyright © 2007 Boeing. All rights reserved. Some Related Work in the Past Boeing Technology | Phantom Works E&IT | Mathematics and Computing Technology • Object-oriented query language, e.g. OQL. • A navigational query paradigm • Exciting features: complex objects, polymorphism, operation invocation, late binding, … • Rule based query language, e.g. Datalog. • Powerful expressiveness, but performance is an issue. • Solid research results on mappings between FOL and Relational calculus. • Solid research results on query optimization • Not trying to replace RDB, but leverage with it Copyright © 2007 Boeing. All rights reserved. More Challenges Boeing Technology | Phantom Works E&IT | Mathematics and Computing Technology • Expressiveness of query specification. • Trade-off between the power of expressiveness and performance. • Mappings • Ontology & underlying data model. • Semantic query primitives & relational query primitives. • Query answer transformation. • How to formulate URIs -- Entity Resolution • A lot of intermediate data needs to be preserved. Performance • Maximize the efficiency of relational query engine – Push down query as much as possible. • Efficient post-query processing. Copyright © 2007 Boeing. All rights reserved.