Models of higher-order, type-safe, distributed computation over autonomous persistent object stores

A remote procedure call (RPC) mechanism permits the calling of procedures in another address space. RPC is a simple but highly effective mechanism for interprocess communication and enjoys nowadays a great popularity as a tool for building distributed applications. This popularity is partly a result of their overall simplicity but also partly a consequence of more than 20 years of research in transpaxent distribution that have failed to deliver systems that meet the expectations of real-world application programmers. During the same 20 years, persistent systems have proved their suitability for building complex database applications by seamlessly integrating features traditionally found in database management systems into the programming language itself. Some research. effort has been invested on distributed persistent systems, but the outcomes commonly suffer from the same problems found with transparent distribution. In this thesis I claim that a higher-order persistent RPC is useful for building distributed persistent applications. The proposed mechanism is: realistic in the sense that it uses current technology and tolerates partial failures; understandable by application programmers; and general to support the development of many classes of distributed persistent applications. In order to demonstrate the validity of these claims, I propose and have implemented three models for distributed higher-order computation over autonomous persistent stores. Each model has successively exposed new problems which have then been overcome by the next model. Together, the three models provide a general yet simple higher-order persistent RPC that is able to operate in realistic environments with partial failures. The real strength of this thesis is the demonstration of realism and simplicity. A higherorder persistent RPC was not only implemented but also used by programmers without experience of programming distributed applications. Furthermore, a distributed persistent application has been built using these models which would not have been feasible with a traditional (non-persistent) programming language

A Multimedia Prototype for Annotation and Illustration Using the Microsoft Foundation Class Library and C++

One of the major claims of the object-oriented programming approach is that it facilitates the development of complex programs by allowing reuse of components. Most compilers for object-oriented languages are now supplied with class libraries. In addition to those provided with the compilers, there are many others in the public domain or available from commercial suppliers. Code reuse can be maximised through the exploitation of framework class libraries for creating interactive programs. A framework library can be viewed as providing a skeleton application that can be extended and specialised through class inheritance. The evolution of application frameworks is discussed briefly in Chapter 1 with an objective to utilise one of them to develop a prototype multimedia application for annotation and illustration. This prototype is referred to as Glasgow Graphics and Sound (GGS) in this thesis. GGS deals with externally created vector or bitmap images, graphics primitives and sound objects in any sequence. GGS is designed to provide the end-users with facilities to work on external images with free-hand curves and other graphics tools, record their voice, save everything in one disk file and animate them later, if necessary. GGS has the responsibility to store different objects without knowing in advance the sequence of object types the user will create. The implementation language, C++ does not have any built-in support for object persistence. Hence, a number of techniques and strategies for adding persistence to C++ objects are reviewed in Chapter 2. The Microsoft Foundation Class (MFC) library is selected as the application framework for developing GGS and the serialization mechanism in MFC is chosen to deal with the object persistence issues. Some of the techniques for persistence, discussed in Chapter 2, are powerful but incur unacceptable overheads for lightweight applications. On the other hand, the MFC serialization is found very useful in creating transportable stream of bytes that can be stored in a file and sent away as an e-mail attachment. Chapter 3 presents the serialization internals in MFC and uncovers some undocumented details that are believed to be valuable for other MFC users. From an application programmer's viewpoint, it is straightforward to use the MFC serialization in most cases. However, the actual implementation details are complex. A sample data structure is serialized and analysed step-by-step to explain the MFC serialization mechanism. The user-friendliness of applications comes not only from an iconic user interface but also from a uniform user interface across applications. Some common user interface elements and their importance are discussed in Chapter 4 along with the document/ view architecture in MFC that separates an application's data management code from its user interface code. The multiple document interface (MDI) in GGS is based on this document/view architecture. A case study walkthrough is presented, purely from an end-user's viewpoint, to illustrate a simple use of GGS. The main classes and their hierarchy are drafted in Chapter 4 based on a high-level decomposition of GGS. Chapter 5 presents the final class hierarchy, different drawing operations and other features involving graphics primitives. Template based type-safe collection classes are used in GGS to store pointers to objects of any type. This simplifies the interaction with the document class. Basic drawing operations such as moving, deleting and highlighting graphics primitives on the screen use an efficient raster drawing mode. The implementation of view magnification together with the standard scrolling capabilities in a window is discussed that requires some special techniques. The benefits of trapping some uncommon messages from the operating system are also discussed. Chapter 5 ends with an overview of the printing process and a description of the multi-page printing features in GGS. Chapter 6 starts with a general discussion on bitmaps and metafiles. A bitmap is a complete digital representation of a picture. Each pixel in the image corresponds to one or more bits in the bitmap. A metafile, on the other hand, stores pictorial information as a series of records that correspond directly to the graphics device interface (GDI) calls. GGS can import externally created bitmaps and metafiles and treat them like any other graphic or sound objects. All commercial illustration programs do something similar. However, the motivation for developing GGS is slightly different. GGS allows the users to construct and manipulate a fairly complex picture, adding comments as they go. The process of constructing the picture is saved, not just the final picture. Sound can be an effective form of information and interface enhancement when appropriately used. It can serve purposes other than the transmission of details or factual information