Browsing by discipline "Tietojenkäsittelytiede"

We examine a previously known sublinear-time algorithm for approximating the length of a string’s optimal (i.e. shortest) Lempel-Ziv parsing (a.k.a. LZ77 factorization). This length is a measure of compressibility under the LZ77 compression algorithm, so the algorithm also estimates a string’s compressibility. The algorithm’s approximation approach is based on a connection between optimal Lempel-Ziv parsing length and the number of distinct substrings of different lengths in a string. Some aspects of the algorithm are described more explicitly than in earlier work, including the constraints on its input and how to distinguish between strings with short vs. long optimal parsings in sublinear time; several proofs (and pseudocode listings) are also more detailed than in earlier work. An implementation of the algorithm is provided. We experimentally investigate the algorithm’s practical usefulness for estimating the compressibility of large collections of data. The algorithm is run on real-world data under a wide range of approximation parameter settings. The accuracy of the resulting estimates is evaluated. The estimates turn out to be consistently highly inaccurate, albeit always inside the stated probabilistic error bounds. We conclude that the algorithm is not promising as a practical tool for estimating compressibility. We also examine the empirical connection between optimal parsing length and the number of distinct substrings of different lengths. The latter turns out to be a suprisingly accurate predictor of the former within our test data, which suggests avenues for future work.

The Web has introduced a new technology in a more distributed and collaborative form of communication, where the browser and the user replace the web server as the nexus of communications in a way that after the call establishment through web servers, the communication is performed directly between browsers as peer to peer fashion without intervention of the web servers. The goal of Real Time Collaboration on the World Wide Web (RTCWeb) project is to allow browsers to natively support voice, video, and gaming in interactive peer to peer communications and real time data collaboration. Several transport protocols such as TCP, UDP, RTP, SRTP, SCTP, DCCP presently exist for communication of media and non-media data. However, a single protocol alone can not meet all the requirements of RTCWeb. Moreover, the deployment of a new transport protocol experiences problems traversing middle boxes such as Network Address Translation (NAT) box, firewall. Nevertheless, the current implementation for transportation of non-media in the very first versions of RTCWeb data does not include any congestion control on the end-points. With media (i.e., audio, video) the amount of traffic can be determined and limited by the codec and profile used during communication, whereas RTCWeb user could generate as much as non-media data to create congestion on the networks. Therefore, a suitable transport protocol stack is required that will provide congestion control, NAT traversal solution, and authentication, integrity, and privacy of user data. This master's thesis will give emphasis on the analysis of transport protocol stack for data channel in RTCWeb and selects Stream Control Transmission Protocol (SCTP), which is a reliable, message oriented general-purpose transport layer protocol, operating on top of both IPv4 and IPv6, providing congestion control similar to TCP and additionally, some new functionalities regarding security, multihoming, multistreaming, mobility, and partial reliability. However, due to the lack of universal availability of SCTP within the OS(s), it has been decided to use the SCTP userland implementation. WebKit is an open source web browser engine for rendering web pages used by Safari, Dashboard, Mail, and many other OS X applications. In WebKit RTCWeb implementation using GStreamer multimedia framework, RTP/UDP is utilized for the communication of media data and UDP tunnelling for non-media data. Therefore, in order to allow a smooth integration of the implementation within WebKit, we have decided to implement GStreamer plugins using SCTP userland stack. This thesis work also investigates the way Mozilla has integrated those protocols in the browser's network stack and how the Data Channel has been designed and implemented using SCTP userland stack.

Googlen kehittämä Android on noussut viime vuosina markkinaosuudeltaan suurimmaksi mobiililaitteiden käyttöjärjestelmäksi. Kuka tahansa voi kehittää Androidille sovelluksia, joiden kehittämiseen tarvittavat välineet ovat ilmaiseksi saatavilla. Erilaisia sovelluksia onkin kehitetty jo yli miljoona. Sovellusten laatu on erityisen tärkeää Android-alustalla, jossa kilpailua on runsaasti ja sovellusten hinta niin alhainen, ettei se muodosta estettä sovelluksen vaihtamiselle toiseen. Sovelluskauppa on myös aina saatavilla suoraan laitteesta. Tämä asettaa sovellusten testaamisellekin haasteita. Toisaalta sovellukset tulisi saada nopeasti sovelluskauppaan, mutta myös sovellusten laadun pitäisi olla hyvä. Testityökalujen pitäisi siis olla helppokäyttöisiä, ja tehokkaita. Androidille onkin kehitetty lukuisia testaustyökaluja Googlen omien työkalujen lisäksi. Tässä tutkielmassa tutustutaan Android-sovellusten rakenteeseen, niiden testaamiseen ja Android-alustalla toimiviin automaattisen testauksen työkaluihin. Erityisesti keskitytään yksikkö- ja toiminnallisen testauksen työkaluihin. Yksikkötestityökaluista vertaillaan Androidin omaa yksikkötestikehystä Robolectriciin. Toiminnallisen testauksen työkaluista vertaillaan Uiautomatoria, Robotiumia ja Troydia.

Hypervisors and containers are the two main virtualization techniques that enable cloud computing. Both techniques have performance overheads on CPU, memory, networking, and disk performance compared to bare metal. Unikernels have recently been proposed as an optimization for hypervisor-based virtualization to reduce performance overheads. In this thesis, we evaluate network I/O performance overheads for hypervisor-based virtualization using Kernel-based Virtual Machine (KVM) and the OSv unikernel and for container-based virtualization using Docker comparing the different configurations and optimizations. We measure the raw networking latency and throughput and CPU utilization by using the Netperf benchmarking tool and measure network intensive application performance using the Memcached key-value store and the Mutilate benchmarking tool. We show that compared to bare metal Linux, Docker with bridged networking has the least performance overhead with OSv using vhost-net coming a close second.

Missing user needs and requirements often lead to sub-optimal software products that users find difficult to use. Software development approaches that follow the user-centered design paradigm try to overcome this problem by focusing on the needs and goals of end users throughout the process life cycle. The purpose of this thesis is to examine how three different user-centered design methodologies approach the development of user requirements and determine whether the ideal requirements development processes described in these methodologies are applicable to the practice of the software industry. The results of this investigation are finally used as a guideline for defining a high-level requirements development framework for the IT department of a large multinational company.

Understanding users’ needs and delivering solutions to them is a demanding task that is often based on guesses. Data can be a capable tool in making those guesses more educated, and more importantly, validating them. Developing software is expensive and doing so based on experiences or opinions imposes a big monetary risk. Continuous experimentation introduces an idea where data is used in a systematic manner to reduce these development risks by constantly validating hypotheses providing crucial knowledge whether the innovation is on the right path or not. There are some existing paths in the form of experimentation models, but implementing and adjusting one to fit your specific environment may be difficult. This thesis presents a case study on a mobile application and its journey to using data in the decision making process. We take a look if existing set of written and event data can be utilized and what are the limitations of them. The data reveals there are multiple uncovered lessons to be learned from. We then look at how to take a more systematic approach and apply continuous experimentation practices in the context of the application. Some initial steps along with an experimentation road map and further experiments are presented. We concluded that the key element to initializing continuous experiment practices is to start small and gradually build the knowledge of the team.

Internetin ja tietotekniikan yleistymisen vuoksi ohjelmistokehitys painottuu yhä enemmän yhteistyöhön ja interaktioon. Suunnitelmakeskeisyydestä ollaan siirrytty kohti ketterämpiä menetelmiä, joissa muutoksen ja kommunikaation tärkeys on tiedostettu. Asiakas ja asiakassuhde on erittäin merkittävä komponentti ohjelmistoprojektin onnistumisessa. Nykyaikaisissa ketterissä ohjelmistokehitystiimeissä asiakkaan edustaja on tiiviisti yhteydessä kehittäjiin palaverien tai muun läsnäolon kautta. Asiakkaan tiivis yhteys kehitykseen on keino tehostaa kehitystä ja saada tyydyttävämpiä tuotteita. Vähemmälle huomiolle on kuitenkin jäänyt toteutetun asiakassuhteen vaikutus kaikille projektin osapuolille. Tässä tutkielmassa tarkastellaan ohjelmistokehitystä asiakkaan ja asiakassuhteen näkökulmasta. Aluksi analysoidaan ohjelmistokehityksen peruspiirteitä ja esitellään yleisimpiä ketteriä menetelmiä. Tämän jälkeen esitellään erilaisia tutkimuksia asiakassuhteesta ja analysoidaan niiden tuloksia. Lopuksi luodaan yhteenveto havaituista ongelmista ja esitetään niihin ratkaisuehdotuksia.

Opinnäytetyön tavoitteena oli tutkia modularisoidun, reaaliaikaisesti koulutettavan neuroverkkojärjestelmän toimintaa samankaltaisen, ei-modulaariseen neuroverkkojärjestelmään verrattuna. Tutkimuksen alustaksi luotiin yksinkertainen pelimaailma ja erilaisia koulutusskenaarioita, sekä toteutettiin Texasin yliopistossa kehitetyn rtNEAT-menetelmän päälle rakentuva modulaarinen kontrolliverkkojärjestelmä. Konstruoidun järjestelmän toimintaa verrattiin perus-rtNEAT -järjestelmän toimintaan, erityisesti kiinnitettiin huomiota aiemmin opitun käyttäytymisen muistamiseen. Tutkimuksen tulos osoitti, että opinnäytetyötä varten konstruoitujen järjestelmien välillä ei ollut merkittävää eroa toimintakyvyssä. Tämä johtuu todennäköisesti testiympäristönä käytetyn pelimaailman yksinkertaisuudesta. Mikäli järjestelmissä on merkittäviä eroja esimerkiksi muistiinpalauttamisen suhteen, näiden esille saamiseksi vaadittaisiin lisätutkimusta.

Productivity is an important aspect of any software development project as it has direct implications on both the cost of software and the time taken to produce it. Though software development as a field has evolved significantly during the last few decades in terms of development processes, best practices and the emphasis thereon, the way in which the productivity of software developers is measured has remained comparatively stagnant. Some established metrics focus on a sole activity, such as programming, which paints an incomplete picture of productivity given the multitude of different activities that a software project consists of. Others are more process-oriented — purporting to measure all types of development activities — but require the use of estimation, a technique that is both time-consuming and prone to inaccuracy. A metric that is comprehensive, accurate and suitable in today's development landscape is needed. In this thesis, we examine productivity measurement in software engineering from both theoretical and pragmatic perspectives in order to determine if a proposed metric, implicitly estimated velocity, could be a viable alternative for productivity measurement in Agile and Lean software teams. First, the theory behind measurement — terminology, data types and levels of measurement — is presented. The definition of the term productivity is then examined from a software engineering perspective. Based on this definition and the IEEE standard for validating software quality metrics, a set of criteria for validating productivity metrics is proposed. The motivations for measuring productivity and the factors that may impact it are then discussed and the benefits and drawbacks of established metrics — chief amongst which is productivity based on lines of code written — explored. To assess the accuracy and overall viability of implicitly estimated velocity, a case study comparing the metric to LoC-based productivity measurement was carried out at the University of Helsinki's Software Factory. Two development projects were studied, both adopting Agile and Lean methodologies. Following a linear-analytical approach, quantitative data from both project artefacts and developer surveys indicated that implicitly estimated velocity is a metric more valid than LoC-based measurement in situations where the overall productivity of an individual or team is of more importance than programming productivity. In addition, implicitly estimated velocity was found to be more consistent and predictable than LoC-based measurement in most configurations, lending credence to the theory that implicitly estimated velocity can indeed replace LoC-based measurement in Agile and Lean software development environments.

In this thesis, we describe Forward Sparse Sampling Search, an algorithm that was published in 2010 by Walsh et al., which combines model-based reinforcement learning with sample-based planning. We show how it can be applied to solving an appropriate set of problems, as well as extend the original tests to give a better view on how the parameters of the algorithm work, and to further the understanding of the method. First, we introduce the concept of reinforcement learning, and identify key environments and points of interest where FSSS is applicable. Next, we explain the terminology and relevant theories the method is based on. The aim is to introduce the reader to a powerful tool for control-problems, and show where to apply it and how to parameterize it. After reading this thesis, one is hopefully fitted with dealing with the basic setup and usage of FSSS. In the final sections of the thesis, we report a series of tests which demonstrate how FSSS works in one particular environment - the Paint/Polish world. The tests focus on understanding the effects of various parameters that the method uses, yielding further understanding on how to effectively apply it, analyzing its performance and comparing it to more basic algorithms on the field. The principal theories and proofs will be explained, and possible paths to improve the algorithm will be explored.