The software and knowledge engineering literature defines maintenance strategies for seven main types of knowledge: words; sentences; behavioural knowledge; and meta-knowledge. Meta-knowledge divides into problem solving methods; quality knowledge; fix knowledge; social knowl- 5 edge; and processing activities. There are five main ways in which these seven knowledge types are processed: acquire; operationalise; fault; fix; and preserve. We review systems that contribute to these 7 5 = 35 types of knowledge maintenance. 1 Introduction 10 A general trend in the twentieth century is an increasing level of doubt about the things we speak or write or try to enter into programs. Popper argues that all knowledge is an hypothesis since nothing can ever be ultimately proved; Submitted to the Knowledge Engineering Review page 2 of 73 our currently believed ideas are merely those that have survive active attempts to refute them [89]. Knowledge representation theorists stress that KBs are...

The design and implementation of the initial release of class evolution technology for PJama persistent language is described. This technology supports modifications to individual classes, class hierarchy, and user-defined conversion of data contained in class instances when a modification to this class leads to the change of instance format. PJama evolution technology was evaluated on an application of considerable size and proved to be very helpful for a PJama programmer. 1 Introduction In this paper we report on the issues raised when investigating the ways of and developing the mechanisms for class evolution in PJama. The PJama project, a collaboration between Sun Microsystems Laboratories and the University of Glasgow, is building an orthogonally persistent platform for Java [1, 2]. PJama is the implementation of the programming language Java with mechanisms embedded into the runtime system that support indefinite lifetimes for a program's data. In fact, not all the data of some...

Object-oriented databases (OODBs) are believed to more naturally reflect the behavior and organization of real world objects. However, OODBs are mostly concerned about only the static aspects of object modeling. While real world objects typically may be multi-perspectived and evolve over time by changing classification and behavior, contemporary OODB models typically regard objects as instances of classes in such a way that classification (and thus behavior) is fixed at the time of creation. This paper introduces the notion of an object role to denote a particular perspective of an object, corresponding to a class for which it is an instance. Roles may be dynamically added and removed from objects to reflect the way real world objects classify and evolve over time, and simultaneously change behavior. A category class is a special class which is associated with a predicate, and in this way describe constraints on how objects may evolve, as well as how objects may automaticall...

The persistent object conversion facilities available in the evolution technology for the PJama persistent programming language are described. They include default and custom conversion, and within the latter - bulk and fully controlled conversion. Where the programmer needs to specify transformations different from the default, they are coded in standard Java. During conversion the "old" object graph remains unchanged, that is, substitute objects are not directly reachable from it, which is crucial for comprehensible semantics of evolution code. The authors believe that the present set of facilities is complete, i.e. it is enough to convert any persistent store instead of rebuilding it from scratch. However, the question of whether this can be generally proven is raised. 1 Introduction The problem of schema evolution is important for persistent languages and object-oriented databases. Though the exact details of persistent data and class storage vary significantly between different ...

Schema Modification Management (SMM) is concerned about how schema changes should affect the object base in order to make database objects be compatible with (single or multiple) specifications after change. However, existing work is mostly concerned about the consistent maintenance of object properties over change, with little or no concern for the classification dimension: Different schema versions may define different hierarchical organizations of the domain (class hierarchies), and so that the same object may classify differently when referenced within the context of different schema versions. The fundamental assumption behind the presented approach is that the real world itself, as well as the perception of the real world, is multi-perspectived and evolving. Objects may evolve over time by arbitrarily adding and removing class memberships (denoted object roles), and which may be independently referenced. A schema versioning approach to SMM is adopted which allows multipleversio...

Schema Modification Management (SMM) is concerned about how schema changes should affect the object base in order to make database objects be compatible with specifications after change. However, a particular problem with existing SMM approaches is the lack of concern for schema-level changes (which may involve multiple classes), or semantic dependencies which applies between non-consecutive versions of the schema. The presented approach adopts a schema versioning approach to SMM (allowing multiple schema versions to coexist), and promotes a global perspective of change management: A powerful means is provided for specifying the presence and maintenance of arbitrary semantic relationships between classes and properties as defined for any schema version in the derivation hierarchy. The fundamental assumption is that semantic dependencies between schema versions do not only follows the derivation relationship, but may go in any directions. To ensure the database behaves cons...

ABSTRACT: In this paper, we present our vision on the component based Information Systems (IS) development and propose a definition of an IS component (ISC). For us, an ISC is a particular IS, integrating static, dynamic and integrity rules specifications. The concept of hyperclasses (HCl) is used to implement the static space of an ISC. A HCl is built on a subset of conceptual classes, forming a unit with a defined semantic. The HCls offer a powerful kind of independence between the methods and the schema. They facilitate ISC refinement and integration. All these concepts also introduce kind of modularity in the definition, management and evolution of an IS.

. The Complex Object And Schema Transformation (COAST) project focuses on the design and implementation of a schema evolution support system using the versioning concept both at the instance and at the schema level of object-oriented database management systems (OODBMS). The versioning approach to schema evolution offers a high degree of flexibility. In ordinary systems two elements depend heavily on the database schema, and therefore prevent schema changes in many cases: The database which is stored according to the types specified in the schema and the set of application programs on top of the schema which require certain properties from the instances. The basic idea of the versioning mechanism is to keep the old schema and database state as a version to allow continuous operation of existing application programs. This decouples the schema from existing instances and applications, and allows arbitrary schema updates at any time. The main contributions of this paper include the develo...

Various proposals have been made to extend objectoriented languages and database systems with roles because they allow to weaken strict typing concepts and therefore can provide mechanisms for an object to change its type during its lifetime. But this so-called object migration is not the only advantage offered by a suitable role model. This paper studies the possibilities to use roles for a general change management system that also includes support for schema evolution. OPAQUE, as the selected role model, can be extended with schema update mechanisms in a surprisingly clean and straightforward way including the concepts of versions and views as well. 1. Introduction Three fundamental categories of change can be identified in a database: object updates, object migration, and schema updates. While the first one, changing an object's value, is handled very well the other two are hardly supported by commercially available database systems. Object migration includes all mechanisms to all...

Situated cognition motivates a review of knowledge maintenance. If knowledge is situated, then a symbolic knowledge base will require modification as the situation changes. We examine the AI and software engineering literature which relates to acquiring and changing programs. Based 5 on a reverse engineering of that literature, we see that strategies have been offered to maintain different types of knowledge: words; sentences; behavioural knowledge; and meta-knowledge. Meta-knowledge divides into problem solving methods; quality knowledge; fix knowledge; social knowledge; and processing activities. We see several kinds of processing activities in 10 the literature: acquire; operationalise; fault; fix; and preserve. To date, no single strategy maintains all types of knowledge or performs all processing activities. However, we can say that many of these processing activities perform some kind of search space reflection. We can use this framework as follows. By using the quality knowled...