C. Laasch and M. H. Scholl. Generic Update Operations Keeping Object-Oriented Databases Consistent. In Proc. 2nd GI-Workshop on Information Systems and Artificial Intelligence. Springer, Feb 1992.  Home/Search   Document Details and Download   Summary   Related Articles   Check

....is defined that is used to specify the extension of view classes. An update operator update allows the application of a given update method m to a set of objects passed as parameters. Other update operators (insert et delete) allow the modification of view class extents in a restricted way. In [LS92] the update semantics for an object model including views is defined. Techniques of automatic classification commonly used in knowledge representation systems are integrated to allow the verification of necessary and sufficient conditions defining constraints on object membership to classes in ....

C. Laasch and M. H. Scholl. Generic Update Operations Keeping Object-Oriented Databases Consistent. In Proc. 2nd GI-Workshop on Information Systems and Artificial Intelligence. Springer, Feb 1992.

.... The language for the implementation of the methods is a Turing complete procedural programming language which also can contain expressions of the query language like in O 2 [3] The query language offers generic operations for projection, selection extension, join and set operations, similar to [8]. Query expressions may be object preserving, i.e. the objects of the result set have the same object identifiers as the original objects. They may be object generating, where the objects in the result set have new object identifiers, or value generating, i.e. the result set does not consist of ....

C. Laasch, M. Scholl: "Generic Update Operations Keeping Object-Oriented Databases Consistent." In: R. Studer (ed.): Proc. 2nd GI-Workshop on Information Systems and Artificial Intelligence (IS/KI), Springer, Ulm, 1992.

....source base followed by a projection of the extended base. The extension and projection can be carried out using four object algebraic operators that specify both the virtual schema and its corresponding virtual instance. This simple algebra can express all the view operators proposed in [KR96, LS92, dS95b, KRR95, CTR96, KR96] Keywords: object database systems, views, data model, object algebra, multiple instantiation, database transformation. 1 Introduction Database views are a well known technique used by applications to customize shared data objects without affecting other ....

....(materializing these views would make it clear) In our framework, we cannot create information that is not derived and disallow typical schema database updates. Note that the four algebraic operators (modulo renaming) enable the same kinds of change as the ones from [KR96] or COOL in COCOON [LS92] Our model has the following main features: 1. The identification of an object in a target database (a view) always enables the retrieval of components via referents. This notion was introduced by C. Souza [dS95b] and is extended in the paper with the mechanism of nested referent ....

C. Laasch and M. H. Scholl. Generic Update Operations Keeping Object-Oriented Databases Consistent. In Proc. 2nd GI-Workshop on Information Systems and Artificial Intelligence. Springer, February 1992.

....Four basic algebraic operators express the autho rized transformations against the schema and the data and complete our model. These operators, projection, natural join, join specialization and union, allow to specify views. This simple algebra express most of the view operators proposed in [LS92,dS95b,KRR95,CTR96,KR96,CKMS97] The algebra is expressible in RQL but some restrictions on the parameters of the operators may guarantee referential integrity constraints as well as key attributes on the view. In the sequel, the main assumptions are that views are virtual (as opposed to ....

....a REAL restructuring of the source schema and base. In our framework, we cannot create information that is not derived and disallow typical schema database updates. Note that the four algebraic operators (modulo renaming) enable the same kinds of change as the ones from [KR96] or COOL in COCOON [LS92] Our model has the following main features: 1. The identification of an object in a target database (a view) always enables the retrieval of components via referents. This notion was introduced by C. Souza [dS95b] and is extended in the paper with the mechanism of complex referent ....

C. Laasch and M. H. Scholl. Generic Update Operations Keeping ObjectOriented Databases Consistent. In Proc. 2nd GI-Workshop on Information Systems and Artificial Intelligence. Springer, February 1992.

....Materializing these views would make it clear. In our framework, we cannot create information that is not derived and disable classical schema database update. Note that the five algebraic operators (modulo renaming) enable the same kinds of change as the ones from [KR96] or COOL in COCOON [LS92] In Rudensteiner[KR96] building a view extends a source schema base, the global schema, adding the newly created virtual class in the same class hierarchy. Additional intermediate classes are also inserted for classification purpose. As opposed to our model, there is only an extension phase. ....

C. Laasch and M. H. Scholl. Generic Update Operations Keeping Object-Oriented Databases Consistent. In Proc. 2nd GI-Workshop on Information Systems and Artificial Intelligence. Springer, February 1992.

....is defined that is used to specify the extension of view classes. An update operator update allows the application of a given update method m to a set of objects passed as parameters. Other update operators (insert et delete) allow the modification of view class extents in a restricted way. In [21], the update semantics for an object model including views is defined. Techniques of automatic classification known from knowledge representation systems are integrated to allow the verification of necessary and sufficient conditions defining constraints on object membership to classes in the ....

C. Laasch and M. H. Scholl. Generic Update Operations Keeping Object-Oriented Databases Consistent. In Proc. 2nd GI-Workshop on Information Systems and Artificial Intelligence. Springer, Feb 1992.

....a source schema instance by applying algebraic operators in two steps, a cascade of extension and projection transformations. These operators, natural join, joinspecialization, union and projection, allow the user to specify views. This algebra expresses most of the view operators proposed in [LS92,dS95b,CTR96,KR96] and in [CKMS97] This functional approach allows one to define views from other view(s) In the sequel, the main assumptions are that views are virtual (as opposed to materialized) and may be considered as queries (composed or not) applied against objects of a source database. ....

....is a restructuring of the source schema and instance. In our framework, we cannot create information that is not derived and disallow typical schema database updates. Note that the four algebraic operators (modulo renaming) enable the same kinds of change as the ones from [KR96] or COOL in COCOON [LS92] Our model has the following main features: 1. The identification of an object in a target database (a view) always enables the retrieval of components via referents. 2. The use of complex oids enables us to consider new objects (join on various classes of different kinds, see Couple) as ....

C. Laasch and M. H. Scholl. Generic Update Operations Keeping ObjectOriented Databases Consistent. In Proc. 2nd GI-Workshop on Information Systems and Artificial Intelligence. Springer, February 1992.

.... of functional (database) languages supporting polymorphism, static type inferencing, and orthogonality (e.g. as in Machiavelli [16] or FAD [5] with object oriented data models including objects with subtyping and flexible update facilities (e.g. as in Iris [27] Melampus [17] or COCOON [12]) The key objectives are: ffl an extension of the relational algebra to an object query language. We started from relational algebra in order to preserve the potential for and knowledge on query optimization. ffl static type checking that allows for early error detection and reduction of ....

....can be verified by the static type checker already at compile time, only update statements that fulfill the restrictions are executed. In the COCOON model the semantics of update operations is defined w.r.t. model inherent constraints (e.g. sub typing, class membership, and class predicates) [12]. That is, applying an update operation to a consistent database state returns a consistent state. Similarly, the update operations of BCOOL are defined w.r.t. typing and subtyping constraints. For example, if an object is deleted, dangling references are avoided, and removing or adding instance ....

C. Laasch and M.H. Scholl. Generic update operations keeping objectoriented databases consistent. In Proc. of 2. GI Workshop Information Systems and Artificial Intelligence, pages 40--55, Ulm, Germany, February 1992. IFB 303, Springer Verlag, Heidelberg.

....that holds for the object. Generally, membership in a class with sufficient class predicate is not manipulated explicitly by add remove, but only implicitly by changing function values used in the class predicate. For more details on the effects of updates in connection with class prediactes see [LS91] Set assigns new values to functions. Let e be a variable holding an employee, then set [ salary=3,000 ] e) assigns a new salary to e. Set is used inside of update and insert and is usually written as an assignment (salary(e) 3,000) Type implementors can specify a function specific method ....

....Like in relational systems, queries can be used to define the extents of virtual classes, that is, collections of objects that are derived from some base classes. The presentation was informal and intended to carry over the ideas, not the exact details. A more formal treatment is contained in [LS91] The central idea is that once the query language fulfills some basic requirements, its use for defining updatable views follows quite naturally. Nevertheless, to our knowledge, this is the only object oriented query language with such a view capability. In contrast to other approaches, we can ....

C. Laasch and M.H. Scholl. Generic update operations keeping object-oriented databases consistent. Submitted for publication, July 1991.

....for the definition of the generic concepts of a KL ONE network [20] That way, we have built a bridge between databases and knowledge representation. It is not just the form of graphics that are used to illustrate COCOON schemas; also the semantics of the model, particularly its update semantics [66], is based on automatic classification, the key issue in KL ONE systems [113, 110] The interesting point about this model for our presentation here is that even though the structural part of the model is substantially different from nested relations, the query language can essentially be a nested ....

C. Laasch and M.H. Scholl. Generic update operations keeping object-oriented databases consistent. Submitted for publication, July 1991.

....expressions by corresponding type inference rules. In order to be able to infer result types for union and intersection operations when the arguments have different types, we need a lattice of types to assign the lowest upper bound and greatest lower bound to the results, respectively [SLT91, LS92b, SLR 92] Classification of views can not be solved completely, since subsumption of predicates is undecidable in general. Therefore, we had to implement an incomplete classification algorithm that fails to achieve the lowest possible positioning in some cases. It is, of course, guaranteed ....

....into account, since the data representing the graph is in the objectbase. New algorithms have been designed, implemented, and extensively tested and evaluated in comparison with various others [Jia90a, Jia92c] 7 Publications Outside publications: HS91, Jia89, Jia90b, Jia91, Jia92a, Jia92b, LS92b, SLT91, SLT90, SS90a, SS90b, SS91b, SS91a, SST92, SSW91, Sch92a, Sch92b, Tre91, TS92] Internal reports and non refereed publications: DHL 92, Jia90a, LS92c, RRS92, RS92, TRSB92, TS91] Theses: Boo91, Fie91, Fra91, Fri91, Gar91, Ger90, Goh91, Gro91, Jia92c, Kla91, Kla90, Kri90, Lae91, ....

C. Laasch and M.H. Scholl. Generic update operations keeping objectoriented databases consistent. In Proc. 2nd GI Workshop on Information Systems and Artificial Intelligence (IS/KI), Ulm, February 1992. Springer IFB, Heidelberg.

....and update algebra to meta objects. Consequently, the use of generic update operators as schema evolution and integration language , instead of special purpose schema evolution methods, has the advantage that: i) the functionality of these operators is formally defined with a clear semantics [14] and has no unpredictable side effects; ii) they handle integrity constraints, that is, no update leaves the database in an inconsistent state w.r.t. these constraints. The remaining problem is to propagate the modifications from the schema level down to the data object level. We will show that ....

....names ( handles ) for objects, since objects are typically unnamed, due to the set oriented style of the language. So this is the way how to refer to objects and results of previous algebra expressions. Besides query operators, COOL also provides a collection of generic update operators (cf. [14] for a formal definition) The main advantage of general purpose update operations is that their semantics is known by the system. That is, they maintain model inherent integrity constraints like uniqueness or acyclicity of functions, and class predicates. We will see later how we exploit by this ....

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C. Laasch and M. H. Scholl. Generic update operations keeping object-oriented databases consistent. In Proc. 2nd GI-Workshop on Information Systems and Artificial Intelligence (IS/KI), FAW Ulm, Germany, February 1992.

....is carried out by the necessary and sufficient predicates. Therefore, the semantics of the remove operation is to take the object out of the pmemb sets of the classes contained in bases(class) For a detailed discussion of the motivation and alternatives for the semantics of add and remove see [LS92] 3.3.5 Inverse Functions Derivation of Inverse Functions In a COCOON schema two functions can be defined to be inverses of each other. However, it is sometimes useful to refer to the inverse of a function that is not explicitly defined in the database schema. We provide a shorthand to derive ....

C. Laasch and M.H. Scholl. Generic update operations keeping object-oriented databases consistent. In Proc. of 2. GI Workshop Information Systems and Artificial Intelligence, pages 40--55, Ulm, Germany, February 1992. IFB 303, Springer Verlag, Heidelberg.

....concurrency control, to check preservation of integrity constraints, or to derive update propagation rules, if they are coded in an imperative language. The standard completely lacks an object manipulation language (OML) e.g. in the style of update, delete, and insert statements of SQL (see also (Laasch and Scholl 1992)) ffl OO optimization and query processing: While relational query processing has been investigated thoroughly, there are only initial frameworks for OO query processing and optimization. Up to now, it is not clear how to integrate these first ideas in order to get efficiency for all ODMG ....

.... is primarily concerned with optimization and implementation (a first prototype has been demonstrated already, parts of it are available online on the Web) For the parts presented in this paper, a suite of generic update operations including a bulk update facility in the style of our earlier work (Laasch and Scholl 1992, Laasch and Scholl 1993b) are next to come, so as to offer a basis for the specification of declarative update transactions. This will constitute the CROQUE OML. Furthermore, some details that have already been mentioned throughout the paper need further elaboration, for example the complete ....

Laasch, C. and Scholl, M. H.: 1992, Generic update operations keeping objectoriented databases consistent, Proc. 2nd GI-Workshop on Information Systems and Artificial Intelligence, Springer IFB 303, FAW Ulm, Germany, pp. 40--55.

....under the control of a global integrity monitor. Technically, this effect is automatically achieved by the fact that the delete operation is actually derived from COOL s lose operation that dynamically changes the type of an object: in each LOB i , delete(o) is defined as lose[object i ] o) Laasch and Scholl, 1992; Scholl et al. 1992 ] Therefore, since in the global context object i is not the root of the type lattice, only the local proxy, but not all the other proxies (if any) are removed. Example 13 Consider the deletion of a part object in the first case locally on the production objectbase PDB, ....

C. Laasch and M.H. Scholl. Generic update operations keeping object-oriented databases consistent. In Proc. 2nd GI Workshop on Information Systems and Artificial Intelligence (IS/KI), Ulm, February 1992. Springer IFB.

....in combining set orientation and updates in a deterministic way and try to give a general, model independent solution. Afterwards, the proposed solution can be combined with elementary update operations that are defined with respect to genericity, safety, and ad hoc usability (see for example [20, 23]) Section 2 reviews known problems with set oriented updates in the relational context. It is shown how this generalizes to object oriented models, and that the problem is due to sharing. In Section 3, we develop a generic set iterator for update operations that allows bulk updates with sequences ....

....type is the element type of the set. These are the basic object preserving query operators of our algebra. Other operators, such as join can be derived from them [25, 26] 4. 3 Update operations There are the following three groups of update operations (a formal definition can be found in [20]: Methods are defined by combining the generic query and update operations. They allow to specify more powerful updates with respect to application specific integrity constraints. Assignments ( and set) for changing values of variables and functions. Besides global assignments to variables ....

C. Laasch and M.H. Scholl. Generic update operations keeping object-oriented databases consistent. In Proc. GI Workshop Information Systems and AI, Ulm, Germany, February 1992. IFB 303, Springer Verlag, Heidelberg.

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