3. Classes should hide their data, we call this encapsulation, only providing a small number of controlled methods or functions in the interface for accessing that data. These factors taken together enable separation of interface from implementation. The actual designs of the algorithms employed inside the classes can be changed as better, more efficient algorithms are found. After a design is complete, changes in a class implementation must not affect its interface. The effect on current and future users is then only in terms of efficiency: their applications need not be recoded to take advantage of the new class implementation. The advantages of separation of interface from implementation include rapid prototyping and graceful refinement. See Fig. 3.

Object-Oriented Analysis and Design.

Mit seiner Publikation “One Size Fits All: An Idea Whose Time Has Come and Gone?“ [St05] hat Michael Stonebraker 2005 die Datenbankszene provoziert. Er vertritt dort die These, dass die eingeführten und in vielen Kontexten eingesetzten „traditionellen“ Datenbanksysteme zwar für viele datenzentrische Anwendungen eingesetzt werden, aber keineswegs die optimalen Systeme für viele dieser Anwendungen (OLAP, Stream Processing, XML Datenbanken, wissenschaftliche Datenbanken, Textsuche) sind. In einer späteren Publikation [St07] stellte er sogar die These auf, dass es keine Anwendungen gibt, für die die traditionellen Datenbanksysteme die beste Alternative sind. Er sagte voraus, dass sich in der kommerziellen Welt eine Anzahl unabhängiger spezialisierter „neuer“ Datenbanksysteme aufsplitten werde, die bestenfalls durch ein gemeinsames Frontend verbunden sind.

"One Size Fits All": An Idea Whose Time Has Come and Gone?

The query efficiency of a data structure that stores a set of objects, can normally be assessed by analysing the number of objects, pointers etc. looked at when answering a query. However, if the data structure is too big to fit in main memory, data may need to be fetched from disk. In that case, the query efficiency is easily dominated by moving the disk head to the correct locations, rather than by reading the data itself.

To reduce the number of disk accesses, once can group the data into blocks, and strive to bound the number of different blocks accessed rather than the number of individual data objects read. An R-tree is a general-purpose data structur that stores a hierarchical grouping of geometric objects into blocks. Many heuristics have been designed to determine which objects should be grouped together, but none of these heuristics could give a guarantee on the resulting worst-case query time.

We present the Priority R-tree, or PR-tree, which is the first R-tree variant that always answers a window query by accessing $O((N/B)^{1-1/d} + T/B)$ blocks, where $N$ is the number of $d$-dimensional objects stored, $B$ is the number of objects per block, and $T$ is the number of objects whose bounding boxes intersect the query window. This is provably asymptotically optimal. Experiments show that the PR-tree performs similar to the best known heuristics on real-life and relatively nicely distributed data, but outperforms them significantly on more extreme data.

The Priority R-Tree: A Practically Efficient and Worst-Case-Optimal R-Tree

Designing interfaces or applications that move beyond the bounds of a single device screen enables new ways to engage with digital content. Research addressing the opportunities and challenges of interactions with multiple devices in concert is of continued focus in HCI research. To inform the future research agenda of this field, we contribute an analysis and taxonomy of a corpus of 510 papers in the cross-device computing domain. For both new and experienced researchers in the field we provide: an overview, historic trends and unified terminology of cross-device research; discussion of major and under-explored application areas; mapping of enabling technologies; synthesis of key interaction techniques spanning across multiple devices; and review of common evaluation strategies. We close with a discussion of open issues. Our taxonomy aims to create a unified terminology and common understanding for researchers in order to facilitate and stimulate future cross-device research.

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Cross-Device Taxonomy: Survey, Opportunities and Challenges of Interactions Spanning Across Multiple Devices

Mobile Personal Health Records (PHRs) have achieved a particularly strong market share since the appearance of more powerful mobile devices and popular worldwide mobile application markets such as Apple's App Store and Android's Google Play. However, Android and Apple have a set of recommendations on design and usability targeted towards developers who wish to publish apps in their stores: Android Design Guidelines and iOS Human Interface Guidelines. This paper aims to evaluate compliance with these guidelines by assessing the usability recommendations of a set of 24 selected mobile PHR applications. An analysis process based on a well-known Systematic Literature Review (SLR) protocol was used. The results show that the 24 mobile PHR applications studied are not suitably structured. 46 % of these applications do not use any of the recommended patterns, using instead lists or springboards, which are deprecated patterns for top-level menus. 70 % of the PHRs require a registration to be able to test the application when these interactions should be delayed. Our study will help both PHR users to select user-friendly mobile PHRs and PHR providers and developers to identify the good usability practices implemented by the applications with the highest scores.

Mobile PHRs Compliance with Android and iOS Usability Guidelines

We propose the PATRICIA-hypercube-tree, or PH-tree, a multi-dimensional data storage and indexing structure. It is based on binary PATRICIA-tries combined with hypercubes for efficient data access. Space efficiency is achieved by combining prefix sharing with a space optimised implementation. This leads to storage space requirements that are comparable or below storage of the same data in non-index structures such as arrays of objects. The storage structure also serves as a multi-dimensional index on all dimensions of the stored data. This enables efficient access to stored data via point and range queries. We explain the concept of the PH-tree and demonstrate the performance of a sample implementation on various datasets and compare it to other spatial indices such as the kD-tree. The experiments show that for larger datasets beyond 10^7 entries, the PH-tree increasingly and consistently outperforms other structures in terms of space efficiency, query performance and update performance.

The PH-tree: a space-efficient storage structure and multi-dimensional index

Despite the recent proliferation of new cross-device application frameworks, there is still a lack of sophisticated tools for testing new applications during their development. This paper presents XDSession---a framework for cross-device application development based on a concept of cross-device sessions, not only useful for managing distribution and synchronisation, but also for logging and debugging. Integrated with XDSession are two new tools specifically designed for cross-device testing. First, the session controller supports management and testing of cross-device sessions with connected or simulated devices at run-time. Second, the session inspector enables inspection and analysis of multi-device/multi-user sessions with support for deterministic record/replay of cross-device sessions. We show the utility of XDSession based on a case study of a semester-long course project in which our tools were used by students to reimplement an existing application and extend it with cross-device capabilities.

XDSession: integrated development and testing of cross-device applications

Cross-device application development poses different requirements ranging from the adaptation and distribution of user interfaces, over the migration of application state to the management of data as it is moved around and shared between devices. In particular, the evaluation of multi-device user interfaces becomes a challenge when they are distributed across a range of interaction resources. We present our ongoing work towards a platform for the design and evaluation of cross-device applications that promotes the central concept of a cross-device session useful for both design and evaluation. Our concept enables the tracking and management of the data part of a distributed, multi-device application as it is viewed and updated on different devices as well as the metadata describing the interactions and how the data evolved as a result of them. We illustrate the benefits of our approach for a first cross-device application and discuss how we plan to address the remaining challenges.

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Information Concepts for Cross-device Applications.

Modern information system development faces the problem that applications may have to run on a large number of platforms with vastly different capabilities and resources, often ranging from mobile devices to desktop computers and further This is particularly true of information systems based on object database technologies which nowadays are used at both ends of the spectrum with embedded systems as well as massive scientific databases among their target domains

Adaptive Model-Driven Information Systems Development for Object Databases

In contrast to their relational counterparts, object databases are more heterogeneous in terms of their architecture, data model and functionality. To this day, this heterogeneity poses substantial difficulties when it comes to benchmark or interoperate object databases. While standardisation proposals have been made in the past, they have had limited impact as neither industry nor research has fully adopted them. We believe that one reason for this lack of adoption is that these standards were too restrictive and thus not capable of dealing with the heterogeneity of object databases. In this paper, we propose a uniform interface for access to object databases that is based on a flexible object model and algebra.

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Christoph Zimmerli

Papers

The PH-tree: a space-efficient storage structure and multi-dimensional index

XDSession: integrated development and testing of cross-device applications

Information Concepts for Cross-device Applications.

Adaptive Model-Driven Information Systems Development for Object Databases

A flexible object model and algebra for uniform access to object databases