# Prof. Lumsdaine Collaboration

Collaboration Participants and Affiliation:

- Adobe Collaborator: Sean Parent
- University Collaborator: Andrew Lumsdaine
- Collaboration Project Name: Declarative Models for Software Composition
- University Name: Indiana University
- Proposed Duration of Collaboration:

Nature of Collaboration:

Objectives:

Large-scale software systems today are typically built by composing together smaller-scale objects (or components). This composition process gives rise to large-scale software structures (implicit algorithms and implicit data structures) that are not well understood. Recent work from Adobe indicates that declarative models allow the composition process to be effected in a manner that can be reasoned about in a principled fashion.

Numerous questions remain however. For example:

- With current composition technology, what are the structures formed by large-scale software systems and what are the invariants that govern them?
- How can these structures and invariants be described in a form upon which the computer can operate?
- How can algorithms which transform these structures be modeled such that the valid set of transformations for a given state can be determined?
- What algorithms can be applied to the structures so they are self-correcting when invariants are violated?
- How can both the transformation and correcting algorithms be described such that can be applied generically?
- How do these ideas apply in the case of communicating sequential processes?

Answering these questions, and firmly establishing the theory and practice of declarative approaches to software composition, will be a significant undertaking. Since this approach goes hand in glove with generic programming, it will be an important part (if not the most important part) of the research agenda for my lab for years to come. To launch this new research initiative, I propose to work closely with Adobe during my sabbatical leave on particular projects in this area. This collaboration will result in a deep understanding of the foundational issues in declarative composition of software components.

One project will involve the property model library (Adam).

One way of defining a UI is that it is a system for assisting a user to select a function and provide a valid set of parameters to that function. Given that a function is selected, there remains the problem of assisting the user in providing a valid set of parameters. If we define validity as a predicate, P, on the set of parameters, X, then "assisting" is a function, F, which is a transformation of X, such that P(F(X)) is true.

There are different forms of F that we can specify as "assisting" - for example assume we are given an X such that P(X) is true (we are already in a valid state) and the user changes a single value of X, say x[i]. Then we would like a function, F, such that P(F(X)) is true and F(X)[i] is equal to the user set x[i]. This is a simple form of correction. For this we would also like the system to be idempotent - such that if P(X) then F(X) == X.

Another form of assistance is prediction - if we know the post-conditions of the function for which X describes the parameters then we can incorporate the result into X and the postconditions into the predicate. In this case P(X) implies both a valid set of preconditions but also an accurate prediction of the result of our function. Using the same notion of changing a single value in X, but in this case where the value is part of the result, we can update the parameters to get the desired result.

Important questions for the property model approach to this problem include:

- How does one describe F()?
- What are the forms of F() that are solvable?
- What is the space of solvable definitions?

Generic programming and generic libraries will also constitute an inmportant part of this collaboration. My lab has been making contributions to the upcoming C++0x standard, particularly in the area of concepts. While the addition of concepts to C++ will significantly improve the support for generic programming and generic libraries, it will also require a change in the way generic programming is taught and practiced. Accordingly, we intend to design a teaching subset of C++0x for generic programming and to develop corresponding teaching material. In addition, tool support in the form of a prototype validator for this subset will be developed.

Milestones & Completion Dates:

- Sep 1, 2007: Kickoff
- Dec 1, 2007:
- Mar 1, 2008:
- Jun 1, 2008:
- Sep 1, 2008:

Expected Results and Artifacts:

- Grant proposal submitted to National Science Foundation Science of Design program. Topic: Declarative composition of generic software components.
- Grant proposal submitted to National Science Foundation Computer Systems Research program. Topic: Declarative composition of sequential communicating processes.
- Publication of results to be submitted to appropriate conferences and/or journals (e.g., OOPSLA, ECOOP, LCSD, PLDI, POPL).
- Prootype C++0x teaching subset validator.

Requested Gift Funding (don't post on wiki - handle via e-mail):

Currently no Adobe confidential information is planned to be disclosed. Currently no IU confidential information is planned to be disclosed.

Adobe code which is available under an open source license (see <http://opensource.adobe.com/licenses.html>) will be used. Contributions to this project from IU will be released under the MIT open source license.