Browsing by discipline "Computer science"

As the virtual world grows more complex, finding a standard way for storing data becomes increasingly important. Ideally, each data item would be brought into the computer system only once. References for data items need to be cryptographically verifiable, so the data can maintain its identity while being passed around. This way there will be only one copy of the users family photo album, while the user can use multiple tools to show or manipulate the album. Copies of users data could be stored on some of his family members computer, some of his computers, but also at some online services which he uses. When all actors operate over one replicated copy of the data, the system automatically avoids a single point of failure. Thus the data will not disappear with one computer breaking, or one service provider going out of business. One shared copy also makes it possible to delete a piece of data from all systems at once, on users request. In our research we tried to find a model that would make data manageable to users, and make it possible to have the same data stored at various locations. We studied three systems, Persona, Freenet, and GNUnet, that suggest different models for protecting user data. The main application areas of the systems studied include securing online social networks, providing anonymous web, and preventing censorship in file-sharing. Each of the systems studied store user data on machines belonging to third parties. The systems differ in measures they take to protect their users from data loss, forged information, censorship, and being monitored. All of the systems use cryptography to secure names used for the content, and to protect the data from outsiders. Based on the gained knowledge, we built a prototype platform called Peerscape, which stores user data in a synchronized, protected database. Data items themselves are protected with cryptography against forgery, but not encrypted as the focus has been disseminating the data directly among family and friends instead of letting third parties store the information. We turned the synchronizing database into peer-to-peer web by revealing its contents through an integrated http server. The REST-like http API supports development of applications in javascript. To evaluate the platform s suitability for application development we wrote some simple applications, including a public chat room, bittorrent site, and a flower growing game. During our early tests we came to the conclusion that using the platform for simple applications works well. As web standards develop further, writing applications for the platform should become easier. Any system this complex will have its problems, and we are not expecting our platform to replace the existing web, but are fairly impressed with the results and consider our work important from the perspective of managing user data.

Ohjelmistointensiivisten tuotteiden määrä on jatkuvassa kasvussa. Tarkkaa tilastotietoa ohjelmistointensiivisten tuotteiden osuudesta tai toimialan kasvusta on kuitenkin vaikea tuottaa, koska organisaation päätoimiala määrittää, mille toimialalle mahdollinen talouskasvu merkitään. Yleinen arvio on kuitenkin, että yhä useampi markkinoilla oleva tuote tai palvelu pitää sisällään digitaalisia komponentteja. Tässä tutkielmassa tarkastellaan digitalisaatiota yhteiskunnallisena ilmiönä, jonka vaikutukset näkyvät organisaatioille joskus hyvinkin äkkinäisinä asiakastarpeiden muutoksina. Digitalisaation kiihdyttämässä kilpailutilanteessa palvelujen ja tuotteiden on vastattava asiakkaiden tarpeisiin sekä mieltymyksiin entistä paremmin ja nopeammin. Tämän tutkielman tarkoituksena on, kirjallisuuskatsauksen muodossa, tunnistaa niitä avaintekijöitä, jotka ovat organisaatioiden kilpailukyvyn kannalta keskeisiä. Ohjelmistoprosessilla on keskeinen rooli organisaatioiden kilpaillessa markkinoista. Tutkielmassa käsitellään myös IT-organisaation roolia uusien innovaatioiden sekä liiketoimintamallien kehittämisessä. IT-organisaatio käsitteenä on tässä tutkielmassa joko suuremman organisaation oma IT-yksikkö tai itsenäinen IT-toimija, jonka palveluja toinen organisaatio hyödyntää. Organisaatiolla tarkoitetaan yksityisen tai julkisen sektorin toimijaa. Horisontaalinen johtaminen, organisaation kyvykkyys muutokseen sekä henkilöstön jatkuvan oppisen malli muodostavat perustan organisaation kyvylle vastata kilpailuun. Organisaation kilpailukyvyn kannalta tärkeää on myös, että ohjelmistoprosessi toimii osana organisaation liiketoiminnan kehittämistä. Näin mahdollistetaan uusien innovaatioiden sekä niiden avulla myös aivan uusien liiketoimintamallien synty; digitaalinen transformaatio. Ohjelmistoprosessin kannalta tärkeää on, että sen avulla pystytään tuottamaan asiakkaille nopeasti heitä miellyttäviä tuotteita/palveluja. Asiakkaan parempi tunnistaminen sekä aktivoiminen osaksi ohjelmistoprosessia ovat myös tärkeitä tekijöitä onnistuneiden tuotteiden ja palveluiden saamiseksi markkinoille. ACM Computing Classification System (CCS): [Software and its engineering~Software creation and management] [Applied computing~Business-IT alignment] [Applied computing~IT governance]

The vast amount of data created in the world today requires an unprecedented amount of processing power to be turned into valuable information. Importantly, more and more of this data is created on the edges of the Internet, where small computers, capable of sensing and controlling their environments, are producing it. Traditionally these so-called Internet of Things (IoT) devices have been utilized as sources of data or as control devices, and their rising computing capabilities have not yet been harnessed for data processing. Also, the middleware systems that are created to manage these IoT resources have heterogeneous APIs, and thus cannot communicate with each other in a standardized way. To address these issues, the IoT Hub framework was created. It provides a RESTful API for standardized communication, and includes an execution engine for distributed task processing on the IoT resources. A thorough experimental evaluation shows that the IoT Hub platform can considerably lower the execution time of a task in a distributed IoT environment with resource constrained devices. When compared to theoretical benchmark values, the platform scales well and can effectively utilize dozens of IoT resources for parallel processing.

Test-driven development is a software development method where programmers compose program code by first implementing a set of small-scale tests which help in the design of the system and in the verification of associated code sections. The reversed design and implementation process is unique: traditionally there is no attempt to verify program code that does not yet exist. Applying practices of test-driven design to a software development process-a generally complex activity involving distinct individuals working in an organization-might have an impact not only on the process itself but on the outcome of the process as well. In order to assess whether test-driven development has perceivable effects on elements of software development, a qualitative literature survey, based on empirical studies and experiments in the industry and academia, was performed. The aggregated results extracted from the studies and experiments on eleven different internal and external process, product and resource quality attributes indicate that there are positive, neutral and negative effects. Empirical evidence from the industry implies that test-driven development has a positive, reducing, effect on the number of defects detected in a program. There is also a chance that the code products are smaller, simpler and less complex than equivalent code products implemented without test-driven practices. While additional research is needed, it would seem that the test-driven produced code is easier for the developers to maintain later, too; on average, maintenance duties took less time and the developers felt more comfortable with the code. The effects on product attributes of coupling and cohesion, which describe the relationships between program code components, are neutral. Increased quality occasionally results in better impressions of the product when the test-driven conform better to the end-user tests but there are times when end-users cannot discern the differences in quality between products made with different development methods. The small, unit-level, tests written by the developers increase the overall size of code products since most of the program code statements are covered by the tests if a test-driven process is followed. Writing tests takes time and the negative effects are associated with the effort required in the process. Industrial case studies see negative implications to productivity due to the extra effort but student experiments have not always been able to replicate similar results under controlled conditions.

Operating System-level Virtualization is virtualization technology based on running multiple isolated userspace instances, commonly referred to as containers, on top of a single operating system kernel. The fundamental difference compared to traditional virtualization is that the targets of virtualization in OS-level virtualization are kernel resources, not hardware. OS-level virtualization is used to implement Bring Your Own Device (BYOD) policies on contemporary mobile platforms. Current commercial BYOD solutions, however, don't allow for applications to be containerized dynamically upon user request. The ability to do so would greatly improve the flexibility and usability of such schemes. In this work we study if existing OS-level virtualization features in the Linux kernel can meet the needs of use cases reliant on such dynamic isolation. We present the design and implementation of a prototype which allows applications in dynamic isolated domains to be migrated from one device to another. Our design fits together with security features in the Linux kernel, allowing the security policy influenced by user decisions to be migrated along with the application. The deployability of the design is improved by basing the solution on functionality already available in the mainline Linux kernel. Our evaluation shows that the OS-level virtualization features in the Linux kernel indeed allow applications to be isolated in a dynamic fashion, although known gaps in the compartmentalization of kernel resources require trade-offs between the security and interoperability to be made in the design of such containers.

General-purpose lossless data compression continues to be an important aspect of the daily use of computers, and a multitude of methods and corresponding compression programs has emerged since information theory was established as a distinct area of research by C.E. Shannon shortly after World War II. Shannon and others discovered several theoretical bounds of data compression and it is, for instance, nowadays known that there can be neither a compressor that can compress all possible inputs, nor any mechanism that compresses at least some inputs while preserving the lengths of the incompressible ones. Although it is therefore indisputable that any compressor must necessarily expand some inputs, it is nonetheless possible to limit the expansion of any input to a constant number of bits in worst case. In order to determine how the established theoretical bounds relate to existing compression programs, I examined two popular compressors, GZip and BZip2, and concluded that their behaviour is not optimal in all respects as they may expand inputs in worst case more than theoretically necessary. On the other hand, the examined programs provide very good compression for most realistic inputs rather swiftly, a characteristic that is most likely appreciated by most computer users. Motivated by a review of the most fundamental bounds of data compression, i.e. Kolmogorov Complexity, Entropy and the Minimum Description Length Principle, and further encouraged by our analysis of GZip and BZip2, I propose a generic, pipelined architecture in this thesis that can — at least in theory - be employed to achieve optimal compression in two passes over the input to be compressed. I subsequently put the proposed architecture directly to the test, and use it to substantiate my claim that the performance of compression (boosting) methods can be improved if they are configured for each input anew with a dynamically discovered set of optimal parameters. In a simple empirical study I use Huffman Coding, a classic entropy-based compression method, as well as Move-To-Front Coding (MTF), a compression boosting method designed to exploit locality among source symbols, to demonstrate that the choice of implied source alphabet influences the achieved compression ratio and that different test inputs require different source alphabets to achieve optimal compression.

Network-intensive smartphone applications are becoming increasingly popular. Examples of such trending applications are social applications like Facebook that rely on always-on connectivity as well as multimedia streaming applications like YouTube. While the computing power of smartphones is constantly growing, the capacity of smartphone batteries is lagging behind. This imbalance has created an imperative for energy-efficient smartphone applications. One approach to increase the energy efficiency of smartphone applications is to optimize their network connections via traffic shaping. Many existing proposals for shaping smartphone network traffic depend on modifications on the smartphone OS, applications, or both. However, most modern smartphone OSes support establishing Virtual Private Networks (VPNs) from user-space applications. Our novel approach to traffic shaping takes advantage of this. We modified OpenVPN tunneling software to perform traffic shaping by altering TCP flow control on tunneled packets. Subjecting heterogenous network connections to traffic shaping without insight into traffic patterns causes serious problems to certain applications. One example of such applications are multimedia streaming applications. We developed a traffic identification feature which creates a mapping between Android applications and their network connections. We leverage this feature to selectively opt-out of shaping network traffic sensitive to traffic shaping. We demonstrate this by selectively shaping background traffic in the presence of multimedia traffic. The purpose of the developed traffic shaper is to enhance the energy efficiency of smartphone applications. We evaluate the traffic shaper by collecting network traffic traces and assessing them with an RRC simulator. The four performed experiments cover multimedia streaming traffic, simulated background traffic and concurrent multimedia and background traffic produced by simulation applications. We are able to enhance the energy efficiency of network transmissions across all experiments.

Tutkielmassa tehtiin esitutkimus Oulun kaupungin sähköisen OmaOulu-portaalin päiväkotisivuston käytettävyydestä ja sopivuudesta sen käyttäjien tarpeisiin. Vanhan ja uuden päiväkotisivun ominaisuuksia selvitettiin lasten vanhempien yksilöhaastattelulla. Päiväkodin arkeen tutustuttiin varjostamalla (shadowing) yhtä päiväkodin työntekijää ja sivustoon liittyviä käyttötilanteita kerättiin kontekstisidonnaisen tiedustelun (contextual interview) avulla. Tutkimuksessa haettiin palautetta uusien päiväkotisivujen käytettävyydestä suhteessa vanhoihin päiväkotisivuihin. Taustatieto päiväkodin toiminnasta, käyttötilanteet ja tiedusteluiden paljastamat ongelmat käyttöliittymässä auttavat suunnittelemaan päiväkotisivujen käytettävyyden tutkimusta jatkossa. Tutkielma esittelee joitakin havainnointi- ja haastattelumenetelmiä, joilla voidaan selvittää käyttötilanteita ja käyttäjien tarpeita. Varjostaminen ja kontekstisidonnainen tiedustelu edustavat eri havainnointimenetelmiä. Käyttäjän varjostamisella viitataan tilanteeseen, jossa tutkija selvittää käyttäjän työhön liittyviä asioita seuraamalla hänen toimiaan. Kontekstisidonnaisessa tiedustelussa tutkija ja käyttäjä tutustuvat käyttäjän työhön yhdessä keskustelemalla. Haastattelu voidaan suorittaa kyselyn (questionnaire), etnografisen haastattelun (ethnographic interview) tai kohderyhmähaastattelun (focus groups) avulla. Kyselyt ovat lomakehaastatteluita, joihin vastaajat vastaavat itsenäisesti. Etnografinen haastattelu taas on suullinen yksilöhaastattelu haastateltavan työympäristössä. Kohderyhmähaastatteluissa haastattelutilanteeseen osallistuu yhtä aikaa useita kohderyhmään kuuluvia henkilöitä. Tulosten luotettavuuteen vaikutti se, että kontekstisidonnaisten tiedusteluiden aikana käyttäjät eivät suorittaneet riittävästi aitoja työtehtäviä. Tiedustelutilanne ei myöskään vastannut aitoa työtilannetta siksi, että henkilökunta käyttää todellisuudessa päiväkotisivua vähän aikaa kerrallaan: päivä lasten kanssa on tiivis ja intensiivinen. Näistä syistä johtuen kontekstisidonnainen tiedustelu ei välttämättä ollut tilanteeseen parhaiten sopiva menetelmä. Haastatteluiden tuloksista käy ilmi, että pääosa päiväkodin henkilökunnasta ja vähän yli puolet lasten vanhemmista suhtautuu uuteen päiväkotisivustoon jossakin määrin hyväksyvästi. On kuitenkin vaikeaa arvioida, onko päiväkodin henkilökunnan työtaakka lisääntynyt sivuston ylläpidon vuoksi. Koska pääosa vanhemmille suunnatuista ominaisuuksista on päiväkotisivuston sisällön kuten kuukausitiedotteiden ja tapahtumakalenterin tarkastelua, tulisi tutkia mahdollisuutta lähettää tarpeellinen tieto sähköpostitse. Osa lasten vanhempien tarvitsemista toiminnoista, kuten poissaoloilmoitusten teko, on jatkossakin välttämätöntä hoitaa sähköisesti. Jatkossa tulee suorittaa lisää varjostamistutkimuksia sekä haastatteluita, jotta nähdään, mitä hyötyjä sivuston käyttö tuo käyttäjilleen.

Pichia pastoris and Saccharomyces cerevisiae are two important fungi in both research and industrial applications of protein production and genetic engineering due to the inherent ability. For example, S.cerevisiae can produce important proteins from wide ranged sugar from ligno-cellulose to methanol. Accurate genome-scale metabolic networks (GMNs) of the two fungi can improve biotechnological production efficiency, drug discovery and cancer research. Comparison of metabolic networks between fungi brings a new way to study the evolutionary relationship between them. There are two basic steps for modeling metabolic networks. The first step is to construct a draft model from existing model or softwares such as the pathway tool software and InterProScan. The second step is model simulation in order to construct a gapless metabolic network. There are two main methods for genome-wide metabolic network reconstruction: constraint-based methods and graph-theoretical pathway finding methods. Constraints-based methods used linear equations to simulate the growth under your model with different constraints. Graph-theoretical pathway finding methods use graphic approach to construct the gapless model so that each metabolite can be acquired from either nutritions or the products of other gapless reactions. In my thesis, a new method designed by Pitkänen [PJH+ 14] is used to reconstruct the metabolic networks of Pichia pastoris and Saccharomyces cerevisiae. Five experiments were developed to evaluate the accuracy of the CoReCo method. The first experiment was to analyze the quality of the GMNs of Pichia pastoris and Saccharomyces cerevisiae by comparing with the existing model. The second and third experiments tested the stability of CoReCo constructed under random mutation and random deletion of the protein sequence simulating noisy input data. The next two experiments were done by considering different number of phylogenetic neighbors in the phylogenetic tree. The last experiment tested the effect of the two main parameters (acceptance and rejection thresholds) when CoReCo filled the reaction gaps in the final step.

Artificial agents are commonly used in games to simulate human opponents. This allows players to enjoy games without requiring them to play online or with other players locally. Basic approaches tend to suffer from being unable to adapt strategies and often perform tasks in ways very few human players could ever achieve. This detracts from the immersion or realism of the gameplay. In order to achieve more human-like play more advanced approaches are employed in order to either adapt to the player's ability level or to cause the agent to play more like a human player can or would. Utilizing artificial neural networks evolved using the NEAT methodology, we attempt to produce agents to play a FPS-style game. The goal is to see if the approach produces well-playing agents with potentially human-like behaviors. We provide a large number of sensors and motors to the neural networks of a small population learning through co-evolution. Ultimately we find that the approach has limitations and is generally too slow for practical application, but holds promise for future developments. Many extensions are presented which could improve the results and reduce training times. The agents learned to perform some basic tasks at a very rough level of skill, but were not competitive at even a beginner level.