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SERF: ODMG-Based Generic Re-Structuring Facility *

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SERF: ODMG-Based Generic Re-Structuring Facility * SERF: ODMG-Based Generic Re-structuring Facility E.A. Rundensteiner, K. Clayp o ol, M. Li, L. Chen, X. Zhang, C. Natara jan, J. Jin, S. De Lima, S. Weiner Department of Computer Science Worcester Polytechnic Institute Worcester, MA 01609 tel.: 508 831{5815, fax: 508 831{5776 frundenst,ka jal,mingli,lichen,xinz,chandu,jing,delima,[email protected] such transformations. Research that has b egun to lo ok 1 Overview into the issue of complex changes [Br e96, Ler96] is still The age of information management and with it the limited by providing a xed set of some selected even advent of increasingly sophisticated technologies have if now more complex op erations. kindled a need in the database community and others To address these limitations of the current re- to re-structure existing systems and move forward to structuring technology, we have prop osed the SERF make use of these new technologies. Legacy application framework which aims at providing a richenvironment systems are b eing transformed to newer state-of-the-art for doing complex user-de ned transformations exi- systems, information sources are b eing mapp ed from bly, easily and correctly [CJR98b]. The goal of our one data mo del to another, a diversity of data sources work is to increase the usability and utility of the are b eing transformed to load, cleanse and consolidate SERF framework and its applicability to re-structuring data into mo dern data-warehouses [CR99]. problems b eyond OODB evolution. Towards that end, Re-structuring is thus a critical task for a variety we provide re-usable transformations via the notion of applications. For this reason, most ob ject-oriented of SERF Templates that can be packaged into li- database systems OODB to day supp ort some form of braries, thereby increasing the portability of these re-structuring supp ort [Tec94, Ob j93, BKKK87]. This transformations. We also nowhave a rst cut at pro- existing supp ort of current OODBs [BKKK87, Tec94, viding an assurance of consistency for the users of this Ob j93] is limited to a pre-de ned taxonomy of simple system, a semantic optimizer that provides some p erfor- xed-semantic schema evolution op erations. However, mance improvements via enhanced query optimization such simple changes, typically to individual typ es techniques with emphasis on the re-structuring prim- only, are not sucient for many advanced applications itives [CNR99]. In this demo we give an overview of [Br e96]. More radical changes, such as combining the SERF framework, its current status and the en- two typ es or rede ning the relationship between two hancements that are planned for the future. We also typ es, are either very dicult or even imp ossible to present an example of the application of SERF to a achieve with current commercial database technology domain other than schema evolution, i.e., the web re- [Tec94, Ob j93]. In fact, most OODBs would typically structuring. require the user to write ad-ho c programs to accomplish This work was supp orted in part by the NSF NYI grant IRI 2 OQL-SERF: Our ODMG Based 94-57609. Wewould also like to thank our industrial sp onsors, in System particular, IBM for the IBM partnership award and Informix for software contribution. Sp ecial thanks also go es to the PSE Team 2.1 System Architecture sp eci cally, Gordon Landis, Sam Haradhvala, Pat O'Brien and Breman Thuraising at Ob ject Design Inc. for not only software In order to validate our concept of SERF transforma- contributions but also for providing us with a customized patchof tions [CJR98b], we have develop ed a working system, the PSE Pro2.0 system that exp osed schema-related APIs needed called OQL-SERF [CJR98a]. OQL-SERF serves b oth to develop our to ol. as pro of of concept as well as helps to explore the suit- ability of the ODMG standard as the foundation for a template-based re-structuring framework. For OQL- SERF, we have used an extension of Java's binding of the ODMG mo del as its ob ject mo del, our bind- ing of the Schema Rep ository for the Metadata Dic- tionary and OQL as the database transformation lan- guage. OQL-SERF is written entirely in Java and uses Ob ject Design Inc.'s 100 Pure Java PSE as its p er- user wants to apply the SERF template transformation. sistent store. As part of our development e ort we A type-check ensures that the typ es of the parameters have also built on top of PSE, aschema evolution fa- match and they exist in the system as well as the cility, Schema Evolution Primitive Manager, the correct numb er of parameters are supplied by the user. Schema Rep ository and OQL Query Engine which This is followed by a bind-check which checks the are not directly a part of the SERF system. Figure 1 existence of these actual parameters in the schema on gives the overall architecture of our system. which they are b eing applied by accessing the Schema Rep ository. The SERF template is instantiated using SERF Framework these parameters by replacing each variable with its b ound parameter after all the checks are completed Template Manager User Template successfully. The instantiated SERF template now Interface Processor invokes ts, i.e., wenow call invokes Instantiates corresp onds to pure OQL statemen Template and Editor executes an OQL transformation. The OQL Query Engine uses Semantic Consistency it Template Schema Optimizer Manager vides an interface for the syntax-checking, the Library pro Viewer parsing and the execution of the OQL transformation. uses uses uses Template Library. SERF templates for a particular domain are collected in a Template Library. Searchof Schema Schema Query a template in this library is supp orted via simple key- Repository uses Evolution Engine Primitives word search on all stored parameters of the template h as the input and output parameters, the name, queries operates on suc 1 the contract , and the description. We are currently in Object inheritance and other semantic Repository queries the pro cess of de ning relationships between templates to facilitate a multi- level organization of the template library. OODB System Consistency Manager. The current version of the Figure 1: Architecture of the SERF Framework Consistency Manager deals with b oth the invariant consistency as sp eci ed by the invariants of the ob ject mo del as well as with contractual consistency, i.e., 2.2 To ols for the SERF System the consistency as sp eci ed by the individual contracts Template Pro cessor. The Template Pro cessor is an of a template. As part of the consistency manager, interface between the user and the SERF framework we have develop ed a language for the sp eci cation of for the execution of a template. Figure 2 shows contracts, i.e., the constraints that must be sati ed the steps p erformed by the Template Pro cessor for by the input schema given by the template and also the execution of a SERF template. The template the constraints that must be satis ed at termination pro cessing b egins with the user supplying the input time. The consistency manager uses these contracts parameters. These parameters are a particular Class for the detection of erroneous templates and provides or Property in the application schema to which the a framework for the managementof violations as well as for veri cation. Template inline(className, refAttrName) className = Class Person, refAttrName = Attribute address Semantic Optimizer. The Optimizer is a to ol for Type-check optimizing SERF templates in terms of their execution error The semantic optimizer uses a query graph as pass times. internal representation. The optimization is based Bind-check error its on a semantic analysis of the data dep endencies in this pass Error to User graph, as well as heuristics of pairwise eliminating, can- Instantiate celing or merging schema evolution primitives [CNR99]. inline(Person, address) e have fo cused in particular on the optimization of (, W Pure oql statements olution metho ds. syntax-check ev error pass Application sp eci c to ol: XML Mapp er. In the Execute context of Re-WEB, a system for the generation and 1 This is for the sp eci cation of consistency constraints as Figure 2: Steps for the Execution of a Template. required by the consistency manager. re-structuring of the web based on the SERF system, [CJR98b] K.T. Clayp o ol, J. Jin, and E.A. Run- wehave also develop ed the XML Mapp er, a to ol that densteiner. SERF: Schema Evolution allows us to pro duce xml les using the structure and through an Extensible, Re-usable and Flex- the ob jects present in the ob ject database and vice ible Framework. In Int. Conf. on Infor- versa. The XML Mapp er uses the web semantics we mation and Know ledge Management, pages de ned for the ODMG ob ject mo del [CRCK98]. 314{321, Novemb er 1998. [CNR99] K.T. Clayp o ol, C. Natara jan, and E.A. 2.3 Highlights of the Demo Rundensteiner. CHOP: An Optimizer for We will demonstrate the latest version of our OQL- Schema Evolution Sequences. Technical SERF system using an example to walk through and Rep ort WPI-CS-TR-99-06, Worcester Poly- show its core functionality in terms of the steps of technic Institute, February 1999. execution for a transformation Figure 2 using our 2 library of templates . We will also demonstrate [CR99] K.T. Claypool and E.A.
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