Although “ now ” is expressed in SQL and CURRENT_TIMESTAMP within queries, this value cannot be stored in the database. How ever, this notion of an ever-increasing current-time value has been reflected in some temporal data models by inclusion of database-resident variables, such as “ now ” “ until-changed, ” “**,” “@,” and “-”. Time variables are very desirable, but their used also leads to a new type of database, consisting of tuples with variables, termed a variable database.

Prior research has shown that achieving high levels of software reuse in the presence of repository and object-based computer-aided software engineering (CASE) development methods presents interesting human, managerial and technical challenges. This article presents research that seeks to enhanced software development performance through reuse. We propose automated support for developers who search large repositories for the appropriate reusable software objects. We characterize search for repository objects in terms of a multistage model involving screening, identification, and the subsequent choice between new object construction or reusable object implementation. We propose automated support tools, including ORCA, a software Object Reuse Classification Analyzer, and AMHYRST, an Automated HYpertext-based Reuse Search Tool, that are based on this model. ORCA utilizes a faceted classification approach that can be implemented using hypertext. We also describe an aspect of AMHYRST's architecture which can automatically create hypertext networks that represent and link objects in terms of a number of distinguishing features. We illustrate our approach with an example drawn from a real world object repository.

In spite of the increasing sophistication and power of commercial spreadsheet packages, we still lack a formal theory or a methodology to support the construction and maintenance of spreadsheet models. Using a dual logical/physical perspective, we identify four principal components that characterize any spread sheet model: schema, data, editorial, and binding . We present a factoring algorithm for identifying and extracting these components from conventional spreadsheets with minimal user intervention, and a synthesis algorithm that assists users in the construction of executable spreadsheets from reusable model components. This approach opens new possibilities for applying object-oriented and model management techniques to support the construction, sharing, and reuse of spreadsheet models in organizations. Importantly, our approach to model management and the Windows-based prototype that we have developed are designed to coexist with, rather than replace , traditional spreadsheet programs. In other words, the users are not required to learn a new modeling language; instead, their logical models and data sets are extracted from their spreadsheets transparently, as a side-effect of using standard spreadsheet programs.