Data of interest to biomedical researchers associated with the Human Genome Project (HGP) is stored all over the world in a number of different electronic data formats and accessible through a varietyof interfaces and retrieval languages. These data sources include conventional relational databases with SQL interfaces, formatted text files on top of which indexing is provided for efficient retrieval (ASN.1-Entrez), and binary files that can be interpreted textually or graphically via special purpose interfaces (ACeDB). Researchers within the HGP wanttocombine data from these different data sources, add value through sophisticated data analysis techniques (such as the biosequence comparison software BLAST and FASTA), and view it using special purpose scientific visualization tools. However, currently there are no commercial tools for enabling such an integrated digital library, and a fundamental barrier to developing such tools appears to be one of language design and optimization: The data f...

In order to find a static type system that adequately supports database languages, we need to express the most general type of a program that involves database operations. This can be achieved through an extension to the type system of ML that captures the polymorphic nature of field selection, together with a technique that generalizes relational operators to arbitrary data structures. The combination provides a statically typed language in which generalized relational databases may be cleanly represented as typed structures. As in ML types are inferred, which relieves the programmer of making the type assertions that may be required in a complex database environment. These extensions may also be used to provide static polymorphic typechecking in object-oriented languages and databases. A problem that arises with object-oriented databases is the apparent need for dynamic typechecking when dealing with queries on heterogeneous collections of objects. An extension of the type system needed for generalized relational operations can also be used for manipulating collections of dynamically typed values in a statically typed language. A prototype language based on these ideas has been implemented. While it lacks a proper treatment of persistent data, it demonstrates that a wide variety of database structures can be cleanly represented in a polymorphic programming language.

We propose a framework for the specification of extensible database systems. A particular goal is to implement a software component for parsing and rule-based optimization that can be used with widely varying data models and query languages as well as representation and query processing systems. The key idea is to use second-order signature (and algebra), a system of two coupled many-sorted signatures, where the top-level signature offers kinds and type constructors and the bottom-level signature provides polymorphic operations over the types defined as terms of the top level. Hence the top level can be used to define a data or representation model and the bottom level to describe a query algebra or a query processing algebra. We show the applicability of this framework by examples drawn from relational modeling and query processing.

Data Types New base types can be added to the EXTRA data model via the EXTRA abstract data type facility. To add a new ADT, the person responsible for adding the type begins by writing (and debugging) the code for the type in the E programming language. E is an extension of C++ [Stro86] that was developed as part of the EXODUS project. E serves as the implementation language for access methods and operators for systems developed using EXODUS. It is also the target language for the query compiler, and (most importantly for our purposes here) the language in which base type extensions will be defined. E extends C++ with a number of features to aid programmers in data- 89 base system programming, including "dbclasses" for persistent storage, class generators for implementing "generic" classes and functions, iterators for use as a control abstraction in writing set operations, and built-in class generators for typed files and variable-length arrays [Rich87]. Suppose that we wanted to add...

We present a typed polymorphic calculus that supports a general mechanism for view definition and object sharing among classes. In this calculus, a class can contain inclusion specifications of objects from other classes. Each such specification consists of a em predicate determining the subset of objects to be included and a viewing function under which those included objects are manipulated. Both predicates and viewing functions can be any type consistent programs definable in the polymorphic calculus. Inclusion specifications among classes can be cyclic, allowing mutually recursive class definitions. These features achieve flexible view definitions and wide range of class organizations in a compact and elegant way. Moreover, the calculus provides a suitable set of operations for views and classes so that the programmer can manipulate views and classes just the same way as one deals with ordinary records and sets. The proposed calculus uniformly integrates views and classes in a polymorphic type system of a database programming language similar to Machiavelli. The calculus has a type inference algorithm that relieves the programmer from complicated type declarations of views and classes. The polymorphic type system of the calculus is also shown to be sound, which guarantees complete static check of type consistency of programs involving classes and views. Through these properties, the programmer can enjoy full advantages of polymorphism and type inference when writing object-oriented database programs.

The Collection Programming Language (CPL) 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. 1 Introduction A vast amount of data currently exists in databases, files formatted according to various data exchange formats, and application programs. Although much of t...

A framework using so called second-order signature for the specification of database models has been presented in earlier work. The goal of this approach is to provide generic tools for the implementation of database systems, in particular for parsing and rule-based optimization and for execution of query plans, that can be used with widely varying data models and query languages. In this paper we apply this specification technique to the graph based data model GraphDB. We develop an algebraic description for the querying facilities of GraphDB and use second-order signature to specify the GraphDB data model and its algebra.

Reflection has been used to address many different problem areas, and the term reflection has itself been used to describe several distinct processes. This paper identifies three simple operations, generation, raising and dynamic rebinding, which may be composed to yield several varieties of reflection. These can be used to allow a self-contained programming system to evolve, through the incorporation of new behaviour into either the application programs or the interpreter which controls their execution. Reflection is a powerful mechanism and potentially dangerous. Used in the context of persistent programming systems, safety is an important consideration: the integrity of large amounts of data may be at stake. This has led to the use of type checking in conjunction with reflection in such systems to provide some guarantees of safety. The paper describes the nature of reflection in persistent systems and identifies some example applications. 1

The possibility of finding a static type system for object-oriented programming languages was initiated by Cardelli [Car88, CW85] who showed that it is possible to express the polymorphic nature of functions such as