Nearly all modern software applications, from the simplest website user account system to the most complex, enterprise-level, completely-integrated infrastructure, utilize some sort of backend data storage and business logic that interacts with the backend. The ubiquitous nature of this backend/business dichotomy makes sense as the need to both store and manipulate data can be traced as far back as the Turing Machine in Computer Science. The most commonly used technologies for these two aspects are Relational Database Management Systems (RDBMS) for backend and Object-Oriented Programming (OOP) for business logic. However, these two methodologies are not immediately compatible and the inherent differences between data represented in RDBMS and data represented in OOP are not trivial. Taking a .NET developer’s perspective, this report aims to explore the RDBMS/OO dichotomy and its inherent issues. Schema management theory and algebra are discussed to gain better perspective of the domain and a survey of existing solutions for the .NET environment is explored. Additionally, methods outside the mainstream are discussed. The advantages and disadvantages of each are weighed and presented to the reader to help aid in design implementations in the future. / text

Researchers and practitioners alike have long sought to integrate programming languages and databases. Today's integration solutions focus on the data-types of the two domains, but today's programs lack transparency. A transparently persistent program operates over all objects in a uniform manner, regardless of whether those objects reside in memory or in a database. Transparency increases modularity and lowers the barrier of adoption in industry. Unfortunately, fully transparent programs perform so poorly that no one writes them. The goal of this dissertation is to increase the performance of these programs to make transparent persistence a viable programming paradigm. This dissertation contributes two novel techniques that integrate programming languages and databases. Our first contribution--called query extraction--is based purely on program analysis. Query extraction analyzes a transparent, object-oriented program that retrieves and filters collections of objects. Some of these objects may be persistent, in which case the program contains implicit queries of persistent data. Our interprocedural program analysis extracts these queries from the program, translates them to explicit queries, and transforms the transparent program into an equivalent one that contains the explicit queries. Query extraction enables programmers to write programs in a familiar, modular style and to rely on the compiler to transform their program into one that performs well. Our second contribution--called RBI-DB+--is an extension of a new programming language construct called a batch block. A batch block provides a syntactic barrier around transparent code. It also provides a latency guarantee: If the batch block compiles, then the code that appears in it requires only one client-server communication trip. Researchers previously have proposed batch blocks for databases. However, batch blocks cannot be modularized or composed, and database batch blocks do not permit programmers to modify persistent data. We extend database batch blocks to address these concerns and formalize the results. Today's technologies integrate the data-types of programming languages and databases, but they discourage programmers from using procedural abstraction. Our contributions restore procedural abstraction's use in enterprise applications, without sacrificing performance. We argue that industry should combine our contributions with data-type integration. The result would be a robust, practical integration of programming languages and databases. / text

The technology of object oriented databases was introduced to system developers in the late 1980?s. Despite that it is rarely used today. This thesis introduces the concept of object oriented databases as the purposed solution to the problems that exist with the use of relational databases. The thesis points to the advantages with storing the application objects in the database without disassembling them to fit a relational data model. Based on that advantages and the cost of introducing such a rarely used technology into a project, a guideline for when to use object oriented databases and when to use relational databases is given. / anders@actk.net

Wound Field Synchronous Generators provide more than 95% of the electricity need worldwide. Their primacy in electricity production is due to ease of voltage regulation, performed by simply adjusting the direct current intensity in their rotor winding. Nevertheless, the rapid progress of power electronics devices enables new possibilities for alternating current add-ins in a more than a century long DC dominated technology. Damping the rotor oscillations with less energy loss than before, reducing the wear of the bearings by actively compensating for the mechanic unbalance of the rotating parts, speeding up the generator with no need for additional means, these are just few of the new applications which imply partial or total alternated current supplying of the rotor winding. This thesis explores what happens in a winding traditionally designed for the direct current supply when an alternated current is injected into it by an inverter. The research focuses on wound field salient pole synchronous machines and investigates the changes in the field winding parameters under AC conditions. Particular attention is dedicated to the potentially harmful voltage surges and voltage gradients triggered by voltage-edges with large slew rate. For this study a wide frequency band simplified electromagnetic model of the field winding has been carried out, experimentally determined and validated. Within the specific application of the fast field current control, the research provides some references for the design of the rotor magnetic circuit and of the field winding. Finally the coordination between the power electronics and the field winding properties is addressed, when the current control is done by means of a long cable or busbars, in order to prevent or reduce the ringing.