The ability to construct a software system from separate pieces while the system is being used is a feature which has become more prevalent and important in recent years; in fact, the ability to dynamically compose a system has existed in various programming languages and computing systems for some time. We use the term dynamically composed systems to refer to systems with this property. In general, dynamically composed systems suffer a number of problems, not the least of which is the difficulty in ascertaining what pieces comprise a system. Furthermore, the definition of how particular pieces are selected, what a consistent collection of pieces is, and how multiple versions of the same piece are handled when composing a system dynamically is typically ambiguous, and feedback to users or maintainers of the system with respect to these issues is often non-existent or too late. Traditional configuration management tools address such system composition and evolution issues, but only in a s...

Problems with the inconsistent behaviour of system construction components for building large and long-lived application systems are identified. They make the programmer's task harder and the user's world more confusing in the same way that the disharmonies between programming languages and databases did. Persistent programming languages overcame those disharmonies. This paper challenges researchers to design and build a common substrate to the construction components. The construction components would be re-built using the substrate to achieve consistent behaviour. Application systems would then use this new family of construction components. The substrate, called the Scalable Persistent Foundation promises several advantages: consistent application system behaviour even when under stress, accelerated application system building and maintenance, genuine longevity of application systems and improved operational efficiency. The search for a design and implementation of this foundation w...

. Research into persistent programming languages and systems in recent years has shown that the technology is useful for developing complex software in many problem domains. This paper explores the issues and consequences of adding persistence to Ada95. The persistence extensions support transparent migration of objects between a program's address space and a persistent store in a way that preserves both type safety and encapsulation of abstract data types. 1 Introduction Ada has recently undergone a major cycle of review and update. The result of this is the new programming language Ada95[12] which is, in the main, backward compatible with Ada83[18]. Two of the principle changes to Ada were the addition of constructs to make it a fully fledged object-oriented language and the use of annexes for defining specialist language capabilities. This paper examines the emerging technology of persistence, and considers how persistent programming can be supported in Ada. We start by introducing...

This paper describes proposed extensions to the Ada95 programming language to provide support for persistent programming. The extensions support transparent migration of data between a program's address space and a persistent store in a way that preserves both type safety and encapsulation of ADT's. 1 Introduction Ada has recently undergone an intensive and major review and update. The result of this is the new programming language Ada95 (ISO 1995) which is, in the main, backward compatible with Ada83. Two of the principle changes to Ada was the addition of appropriate semantic constructs to change Ada from an objectbased language to a fully fledged object-oriented language and the provision of annexes defining additional language capabilities for specific user communities. In this paper we consider further extensions to Ada95 by way of the introduction of a persistence annex to provide persistent programming support to Ada. We call this revision persistent Ada95 to distinguish it fr...

Practice has proven that databases are the keystones for nearly all application systems with a wider functionality, utilization and availabilty. As a consequence, next generation database systems will have to provide their services with a degree of interoperability that has to be substantially improved over existing solutions. In this paper we argue that this objective can be achieved only through full exploitation of current developments in computer language technology.

Persistent systems support a single storage abstraction in which all data may be created and manipulated in a uniform manner, regardless of its longevity. In such systems a protection mechanism is required to ensure that programs can access precisely those objects they are supposed to access and no others. In a monolingual system this protection can be provided by the type system of the programming language; in systems which support multiple persistent languages a separate protection mechanism must be supported. This paper describes the capability-based protection mechanism employed in Grasshopper, a new operating system specifically designed to support persistent systems on a conventional workstation platform. We show that this mechanism provides sufficient power and flexibility to handle a wide variety of protection scenarios. 1.

Adaptive data is characterised by its ability to react to changes in the environment. Such data frequently occurs in Artificial Intelligence applications where the knowledge base may alter dynamically to adapt to new stimuli. Such systems are usually written in typeless, dynamically bound languages. Here we describe the concept of persistence and show how it may also be used in conjunction with a strong type system employing flexible binding mechanisms to construct adaptive systems. This has the advantage of greater static checking with all of its attendant benefits, without losing flexibility. Keywords and phrases: persistence, strong typing, dynamic binding, production systems, adaptive systems. 1. Introduction A popular topic for speculation in recent times is how Artificial Intelligence (A.I.) techniques may be used in the management of large software projects [7]. For example, the searching of component libraries in version control and configuration management systems ...

. Research into persistent programming languages and systems in recent years has shown that the technology is useful for developing complex software in many problem domains. This paper explores the issues and consequences of adding persistence to Ada95. The persistence extensions support transparent migration of objects between a program's address space and a persistent store in a way that preserves both type safety and encapsulation of abstract data types. Keywords and Phrases: Kinds of systems: persistent systems; Ada95; object-oriented technology. 1 Introduction Ada has recently undergone an intensive and major review and update. The result of this is the new programming language Ada95[23] which is, in the main, backward compatible with Ada83[36]. Two of the principle changes to Ada were the addition of new constructs to change it from an object-based language to a fully fledged object-oriented language and the provision of annexes defining additional language capabilities for spec...

Persistent programming languages provide abstract mechanisms which completely describe the storage and retrieval of long term data. In this paper, the Ten15 persistent programming language is reviewed. Ten15 can be categorised as supporting a minimal persistence mechanism and an extremely powerful and expressive type system. Details of using Ten15 to build a general purpose filing system, based on dictionaries, are given. It is concluded that the ability to build a complex and flexible file system depends on two factors: the constructive power of the type system and the flexibility of the minimal persistent store. ############### * Research is sponsored by SERC/UK research grant number 89556293 and with the support of the Procurement Executive Ministry of Defence. 1. Introduction Persistence is the ability for program data to endure longer than the invocation of the program which creates it [2]. It has formed the basis for a large research community which has identified the underly...

Data Types ............................................45 11.1 Abstract Data Type Definition ................................... 45 11.2 Creation of Abstract Data Objects............................... 45 11.3 Use of Abstract Data Objects .................................... 46 11.4 Equality and Equivalence ........................................ 47 12 Files .............................................................48 12.1 File Literal ......................................................... 48 12.2 Equality and Equivalence ........................................ 48 13 Type any ........................................................49 13.1 Injection into Type any........................................... 49 13.2 Projection from Type any........................................ 49 13.3 Equality and Equivalence ........................................ 50 14 Environments ...................................................51 14.1 Creating a New Environment.......................