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Research and Advances Sep 1 1985

Data structures for quadtree approximation and compression

A number of data structures for representing images by quadtrees without pointers are discussed. The image is treated as a collection of leaf nodes. Each leaf node is represented by use of a locational code corresponding to a sequence of directional codes that locate the leaf along a path from the root of the tree. Somewhat related is the concept of a forest which is a representation that consists of a collection of maximal blocks. It is reviewed and refined to enable the representation of a quadtree as a sequence of approximations. In essence, all BLACK and WHITE nodes are said to be of type GB and GW, respectively. GRAY nodes are of type GB if at least two of their sons are of type GB; otherwise, they are of type GW. Sequences of approximations using various combinations of locational codes of GB and GW nodes are proposed and shown to be superior to approximation methods based on truncation of nodes below a certain level in the tree. These approximations have two important properties. First, they are progressive in the sense that as more of the image is transmitted, the receiving device can construct a better approximation (contrast with facsimile methods which transmit the image one line at a time). Second, they are proved to lead to compression in the sense that they never require more than MIN(B, W) nodes where B and W correspond to the number of BLACK and WHITE nodes in the original quadtree. Algorithms are given for constructing the approximation sequences as well as decoding them to rebuild the original quadtree.
Research and Advances Aug 1 1985

Data-flow algorithms for parallel matrix computation

In this article we develop some algorithms and tools for solving matrix problems on parallel processing computers. Operations are synchronized through data-flow alone, which makes global synchronization unnecessary and enables the algorithms to be implemented on machines with very simple operating systems and communication protocols. As examples, we present algorithms that form the main modules for solving Liapounov matrix equations. We compare this approach to wave front array processors and systolic arrays, and note its advantages in handling missized problems, in evaluating variations of algorithms or architectures, in moving algorithms from system to system, and in debugging parallel algorithms on sequential machines.
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Research and Advances Aug 1 1985

ALGLIB, a simple symbol-manipulation package

ALGLIB—a library of procedures that perform analytic differentiation and other simple symbolic manipulations—has certain advantages over existing and more comprehensive packages. It can be implemented in a high-level language of the user's choice using a pseudocode available from the authors, and it is easily interfaced with the user's programs.
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Research and Advances Aug 1 1985

Database design: composing fully normalized tables from a rigorous dependency diagram

A new simplified methodology for relational-database design overcomes the difficulties associated with nonloss decomposition. It states dependencies between data fields on a dependency list and then depicts them unambiguously as interlinked bubbles and doublebubbles on a dependency diagram. From the dependency diagram, a set of fully normalized tables is derived.
Research and Advances Jul 1 1985

Environmental and institutional models of system development: a national criminal history system

This article tests two competing theories of system development referred to here as environmental and institutional models. These models form the basis for most explanations of why systems are developed and utilized. We will examine both models in detail and apply them to a single set of data concerned with the emerging national computerized criminal history system (CCH). A hybrid model, which combines elements of environmental and institutional approaches, is also developed and tested. A substantive result of this new model will alter our understanding of why a national CCH system is being developed. At the theoretical level, we conclude that a hybrid model is more powerful than either an environmental or an institutional model taken separately and that future research must take this into account.

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