A software system has dynamic adaptability if it can adapt itself to dynamically changing runtime environments. As open-ended distributed systems and mobile computing systems have spread widely, the need for software systems with dynamic adaptability increases. We propose a software model with dynamic adaptability called DAS and its description language LEAD++. The basic mechanism for dynamic adaptability is called adaptable procedure. An adaptable procedure is a special kind of generic procedures (functions) whose methods are selected based upon the state of its runtime environment. Furthermore, control mechanisms of adaptable procedures -- including method selection strategies -- are realized using generic procedures. This sort of reflective architecture enables us to write a dynamically adaptable software system in highly flexible, extensible, readable and maintainable way. LEAD++ is an object-oriented reflective language that provides adaptable procedures and their control mechanisms as its basic language functionalities. We are currently implementing a prototype of LEAD++ as a pre-processor of Java. Using LEAD++, we can systematically describe dynamically adaptable applets, mobile objects, etc.

As open-ended distributed systems and mobile computing systems have spread widely, the need for software which can adapt itself to the dynamic change of runtime environments increases. We call the ability of the software dynamic adaptability. We designed and implemented a language LEAD that provides an architecture for dynamic adaptability. The basic idea is to introduce the mechanism which changes procedure invocation dynamically according to the states of runtime environments. Using LEAD, we can easily realize 1) the highly extensible dynamically adaptable applications, and 2) the introduction of the dynamic adaptability into existing applications.