Querying an Object-Oriented Database Using CPL

The Collection Programming Language is based on a complex value model of data and has successfully been used for querying transforming and integrating data from a wide variety of structured data sources - relational, ACeDB, and ASN.1 among others. However, since there is no notion of objects and classes in CPL, it cannot adequately model recursive types or inheritance, and hence cannot be used to query object-oriented databases (OODBs). By adding a reference type and four operations to CPL - dereference, method invocation, identity test and class type cast - it is possible to express a large class of interesting safe queries against OODBs. As an example of how the extended CPL can be used to query an OODB, we will describe how the extended language has been used as a query interface to Shore databases

A Theory of Tagged Objects

Foundational models of object-oriented constructs typically model objects as records with a structural type. However, many object-oriented languages are class-based; statically-typed formal models of these languages tend to sacrifice the foundational nature of the record-based models, and in addition cannot express dynamic class loading or creation. In this paper, we explore how to model statically-typed object-oriented languages that support dynamic class creation using foundational constructs of type theory. We start with an extensible tag construct motivated by type theory, and adapt it to support static reasoning about class hierarchy and the tags supported by each object. The result is a model that better explains the relationship between object-oriented and functional programming paradigms, suggests a useful enhancement to functional programming languages, and paves the way for more expressive statically typed object-oriented languages. In that vein, we describe the design and implementation of the Wyvern language, which leverages our theory

Introduction to the Literature On Programming Language Design

This is an introduction to the literature on programming language design and related topics. It is intended to cite the most important work, and to provide a place for students to start a literature search

Type Safe Extensible Programming

Software products evolve over time. Sometimes they evolve by adding new features, and sometimes by either fixing bugs or replacing outdated implementations with new ones. When software engineers fail to anticipate such evolution during development, they will eventually be forced to re-architect or re-build from scratch. Therefore, it has been common practice to prepare for changes so that software products are extensible over their lifetimes. However, making software extensible is challenging because it is difficult to anticipate successive changes and to provide adequate abstraction mechanisms over potential changes. Such extensibility mechanisms, furthermore, should not compromise any existing functionality during extension. Software engineers would benefit from a tool that provides a way to add extensions in a reliable way. It is natural to expect programming languages to serve this role. Extensible programming is one effort to address these issues. In this thesis, we present type safe extensible programming using the MLPolyR language. MLPolyR is an ML-like functional language whose type system provides type-safe extensibility mechanisms at several levels. After presenting the language, we will show how these extensibility mechanisms can be put to good use in the context of product line engineering. Product line engineering is an emerging software engineering paradigm that aims to manage variations, which originate from successive changes in software.Comment: PhD Thesis submitted October, 200

Simple objects for Standard ML

This paper proposes a new approach to adding objects to the statically-typed, higher-order language Standard ML. Our approach sacrifices some of the expressiveness found in recently proposed schemes for typing object-oriented features, but by doing so, we avoid a tremendous amount of complexity in the type system. In fact, our system is a conservative extension of the SML type system, and preserves the important properties of SML: sound static typing, and type inference. Our approach is based on introducing object types, which have an explicitly declared subtyping hierarchy, and object constructors. Just as datatype constructors are used to guide type inference of recursive types, we use object type constructors to guide the inference of subtyping. The introduction of object constructors also has the effect of generalizing the SML case statement to be a typecase on object types. Using this mechanism, we can often recover type information that our type system cannot preserve statically...