This doctoral thesis examines the history of the Iraqw’ar Da/aw area in the Mbulu Highlands of northern Tanzania. Since the late nineteenth century this area has been known for its intensive cultivation, and referred to as an “island” within a matrix of less intensive land use. The conventional explanation for its characteristics has been high population densities resulting from the prevention of expansion by hostility from surrounding pastoral groups, leading to a siegelike situation. Drawing on an intensive programme of interviews, detailed field mapping and studies of aerial photographs, early travellers’ accounts and landscape photographs, this study challenges that explanation. The study concludes that the process of agricultural intensification has largely been its own driving force, based on self-reinforcing processes of change, and not a consequence of land scarcity.

This report presents RACR, a reference attribute grammar library for the programming language Scheme. RACR supports incremental attribute evaluation in the presence of abstract syntax tree rewrites. It provides a set of functions that can be used to specify abstract syntax tree schemes and their attribution and construct respective trees, query their attributes and node information and annotate and rewrite them. Thereby, both, reference attribute grammars and rewriting, are seamlessly integrated, such that rewrites can reuse attributes and attribute values change depending on performed rewrites – a technique we call Reference Attribute Grammar Controlled Rewriting. To reevaluate attributes influenced by abstract syntax tree rewrites, a demand-driven, incremental evaluation strategy, which incorporates the actual execution paths selected at runtime for control-flows within attribute equations, is used. To realize this strategy, a dynamic attribute dependency graph is constructed throughout attribute evaluation – a technique we call Dynamic Attribute Dependency Analyses. The report illustrates RACR's motivation, features, instantiation and usage. In particular its application programming interface is documented and exemplified. The report is a reference manual for RACR developers. Further, it presents RACR’s complete implementation and therefore provides a good foundation for readers interested into the details of reference attribute grammar controlled rewriting and dynamic attribute dependency analyses.

情報処理学会研究報告. SLP, 音声言語情報処理;　98-SLP-24-5

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El propósito de esta Tesis es llevar a cabo un proceso en el que se aplique la práctica de la integración continua en un desarrollo de software dirigido por modelos de forma eficiente, mediante el cual los desarrollos de software puedan beneficiarse conjuntamente de las mejoras y ventajas que proporcionan la aproximación de desarrollo de la ingeniería dirigida por modelos y la práctica de la integración continua. La aproximación de la ingeniería dirigida por modelos es el último salto natural de la ingeniería del software en cuanto a la búsqueda de métodos de desarrollo que elevan el nivel de abstracción hasta el punto en el que los expertos de un dominio de conocimiento, ajenos al mundo informático, son capaces de guiar y cambiar la lógica de los sistemas informáticos. La práctica de la integración continua es una recomendación de las principales metodologías de desarrollo, que tiene como objetivo la realización de integraciones automáticas del software en etapas tempranas del desarrollo, ofreciendo ventajas como la reducción del riesgo intrínseco que, dado su carácter temporal y único, tienen todos los proyectos. Con la unión de la ingeniería dirigida por modelos y de la práctica de la integración continua se busca ofrecer, a los equipos de desarrollo que trabajan utilizando algún tipo de iniciativa de la ingeniería dirigida por modelos, la posibilidad de integrar de forma continua y distribuida sus desarrollos. Al mismo tiempo, los clientes, verdaderos expertos del dominio de conocimiento en su ámbito de negocio, se benefician del aumento del nivel de abstracción de las técnicas de desarrollo para que ellos mismos, y de forma transparente, sean capaces de modificar su propio sistema informático sin la ayuda de personal técnico ajeno a su negocio, ahorrando así tiempo y costes. Para cumplir con el objetivo de esta Tesis doctoral se construye un prototipo que salva los impedimentos actuales que no permiten la unión entre estos dos nuevos activos de la ingeniería del software. Los principales problemas encontrados están relacionados con la selección de una iniciativa de desarrollo apropiada, los sistemas de control de versiones especialmente adaptados para trabajar con modelos, la generación incremental de artefactos a partir de modelos y la adaptación a las herramientas actuales de integración continua de forma optimizada. La separación del trabajo realizado en diferentes bloques permite ofrecer soluciones de forma tanto aislada como en conjunto, dando lugar a un trabajo iterativo e incremental de comienzo a fin. Para analizar las ventajas que ofrece la propuesta de este trabajo frente a otras posibilidades de desarrollo, se realiza una evaluación mediante la creación de diferentes casos de prueba en los que la medición de diferentes parámetros ofrecen una estimación numérica de las ventajas reales obtenidas. El análisis descriptivo, el contraste de hipótesis y las técnicas de regresión permiten una mejor interpretación de los resultados. Finalmente, se define el proceso, objetivo último de este trabajo, mediante la respuesta a diferentes preguntas planteadas, que facilitan su comprensión y entendimiento. / The purpose of this Thesis is to create a process in which the continuous integration practice can be applied to a model-driven software development in an e ective way, through which software developments can bene t jointly and simultaneously from the improvements and advantages provided by the model-driven engineering development approach and the continuous integration practice. The model-driven engineering approach is the last natural step of software engineering in the search for development approaches that raise the level of abstraction to the point that experts in a domain of knowledge, outside the computer world, are able to guide and change the logic of computer systems. The continuous integration practice is a recommendation of the most widely accepted development methodologies that aims to carry out automatic software integrations in early stages of development, o ering bene ts such as reducing the inherent risk that, given its unique nature, every project has. By merging the model-driven engineering and the continuous integration practice, the aim is to provide to development teams that work using some kind of model-driven engineering initiative, the possibility to integrate their developments in a continuous and distributed way. At the same time, customers, the real experts in the domain of knowledge in their eld of business, can bene t from the increased level of abstraction in developing techniques. Thus, they, in a transparent manner, are able to modify their own computer system without the help of external technical sta , so saving time and costs. To meet the objective of this Thesis, a prototype which saves all the current constraints that do not allow the union between these two new tools of software engineering is build. The main problems found were related to the selection of an appropriate development initiative, the version control systems specially adapted to working with models, the incremental generation of artifacts from models, and the optimized adaptation to existing continuous integration tools. The separation of work in di erent blocks can provide solutions, both in isolation or in conjunction, resulting in an iterative and incremental work from beginning to end. To analyze the bene ts of the proposal in this work compared to other development possibilities, an evaluation is performed by creating di erent test cases in which the measurement of di erent parameters can give a numerical estimate of the real bene ts obtained. The descriptive analysis, the hypothesis testing, and regression techniques allow a better interpretation of results. Finally, the process, the main objective of this work, is de ned by answering various questions posed to facilitate its comprehension and understanding.

Disasters due to war and conflict or natural forces are responsible for the 26 million people displaced across the world today. The crisis extends into the temporary, yet indefinite, displacement camps where people live in congested living arrangements, vulnerable to an increased risk of disease, death, and social violence (spousal abuse, rape). Even when chaos subsides, social and physical networks have frayed rendering the temporary displacement camp a permanent home for some. Often, despite this “permanence”, access to adequate services and infrastructure and hence social and economic growth remains in a state of emergency. This thesis proposes that water infrastructure is the key social catalyst for developing these displacement camps into permanent sustainable communities. An urban displacement camp in the town of Gulu, Northern Uganda, is the case study location for a speculative design intervention. During rebel activities from 1996 to 2004, the town of Gulu more than tripled in size, absorbing almost 100,000 displaced people forced to flee their land. These people settled in displacement camps next to, and within the wetlands that border the town on all sides. The urban metabolism of the town has become polluted as the displaced people use, alter and degrade the wetlands because they have no other alternatives. Following the instigation of a peace process in 2006, some people have begun the journey home. However, it is estimated that just over half of these people will continue to live in the squalid camps, without an opportunity to prosper. A strategy is proposed for addressing and subsequently re-defining this urban metabolism. By synthesizing the existing urban fabric with strategies for harnessing the natural landscape, varying scales of water infrastructure are proposed. New opportunities for agricultural production is supported, while the spatial relationships created by the physical structuring of the water infrastructure renews the influence that water collection and distribution has in creating the social locus of a community.

Disasters due to war and conflict or natural forces are responsible for the 26 million people displaced across the world today. The crisis extends into the temporary, yet indefinite, displacement camps where people live in congested living arrangements, vulnerable to an increased risk of disease, death, and social violence (spousal abuse, rape). Even when chaos subsides, social and physical networks have frayed rendering the temporary displacement camp a permanent home for some. Often, despite this “permanence”, access to adequate services and infrastructure and hence social and economic growth remains in a state of emergency. This thesis proposes that water infrastructure is the key social catalyst for developing these displacement camps into permanent sustainable communities. An urban displacement camp in the town of Gulu, Northern Uganda, is the case study location for a speculative design intervention. During rebel activities from 1996 to 2004, the town of Gulu more than tripled in size, absorbing almost 100,000 displaced people forced to flee their land. These people settled in displacement camps next to, and within the wetlands that border the town on all sides. The urban metabolism of the town has become polluted as the displaced people use, alter and degrade the wetlands because they have no other alternatives. Following the instigation of a peace process in 2006, some people have begun the journey home. However, it is estimated that just over half of these people will continue to live in the squalid camps, without an opportunity to prosper. A strategy is proposed for addressing and subsequently re-defining this urban metabolism. By synthesizing the existing urban fabric with strategies for harnessing the natural landscape, varying scales of water infrastructure are proposed. New opportunities for agricultural production is supported, while the spatial relationships created by the physical structuring of the water infrastructure renews the influence that water collection and distribution has in creating the social locus of a community.

Perhaps the most flexible synopsis of a database is a uniform random sample of the data; such samples are widely used to speed up the processing of analytic queries and data-mining tasks, to enhance query optimization, and to facilitate information integration. Most of the existing work on database sampling focuses on how to create or exploit a random sample of a static database, that is, a database that does not change over time. The assumption of a static database, however, severely limits the applicability of these techniques in practice, where data is often not static but continuously evolving. In order to maintain the statistical validity of the sample, any changes to the database have to be appropriately reflected in the sample. In this thesis, we study efficient methods for incrementally maintaining a uniform random sample of the items in a dataset in the presence of an arbitrary sequence of insertions, updates, and deletions. We consider instances of the maintenance problem that arise when sampling from an evolving set, from an evolving multiset, from the distinct items in an evolving multiset, or from a sliding window over a data stream. Our algorithms completely avoid any accesses to the base data and can be several orders of magnitude faster than algorithms that do rely on such expensive accesses. The improved efficiency of our algorithms comes at virtually no cost: the resulting samples are provably uniform and only a small amount of auxiliary information is associated with the sample. We show that the auxiliary information not only facilitates efficient maintenance, but it can also be exploited to derive unbiased, low-variance estimators for counts, sums, averages, and the number of distinct items in the underlying dataset. In addition to sample maintenance, we discuss methods that greatly improve the flexibility of random sampling from a system's point of view. More specifically, we initiate the study of algorithms that resize a random sample upwards or downwards. Our resizing algorithms can be exploited to dynamically control the size of the sample when the dataset grows or shrinks; they facilitate resource management and help to avoid under- or oversized samples. Furthermore, in large-scale databases with data being distributed across several remote locations, it is usually infeasible to reconstruct the entire dataset for the purpose of sampling. To address this problem, we provide efficient algorithms that directly combine the local samples maintained at each location into a sample of the global dataset. We also consider a more general problem, where the global dataset is defined as an arbitrary set or multiset expression involving the local datasets, and provide efficient solutions based on hashing.

Combinatorial problems are ubiquitous in our society and solving such problems efficiently is often crucial. One technique for solving combinatorial problems is constraint-based local search. Its compositional nature together with its efficiency on large problem instances have made this technique particularly attractive. In this thesis we contribute to simplifying the solving of combinatorial problems using constraint-based local search. To provide higher-level modelling options, we introduce set variables and set constraints in local search by extending relevant local search concepts. We also propose a general scheme to follow in order to define what we call natural and balanced constraint measures, and accordingly define such measures for over a dozen set constraints. However, defining such measures for a new constraint is time-consuming and error-prone. To relieve the user from this, we provide generic measures for any set constraint modelled in monadic existential second-order logic. We also theoretically relate these measures to our proposed general scheme, and discuss implementation issues such as incremental algorithms and their worst-case complexities. To enable higher-level search algorithms, we introduce constraint-directed neighbourhoods in local search by proposing new constraint primitives for representing such neighbourhoods. Based on a constraint, possibly modelled in monadic existential second-order logic, these primitives return neighbourhoods with moves that are known in advance to achieve a decrease (or preservation, or increase) of the constraint measures, without the need to iterate over any other moves. We also present a framework for constraint-based local search where one can model and solve combinatorial problems with set variables and set constraints, use any set constraint modelled in monadic existential second-order logic, as well as use constraint-directed neighbourhoods. Experimental results on three real-life problems show the usefulness in practice of our theoretical results: our running times are comparable to the current state-of-the-art approaches to solving the considered problems.