Punainen kirja kaupungeista

Kirjallisuusarvostelu

Formal modelling for digital media distribution

Human beings have always strived to preserve their memories and spread their ideas. In the beginning this was always done through human interpretations, such as telling stories and creating sculptures. Later, technological progress made it possible to create a recording of a phenomenon; first as an analogue recording onto a physical object, and later digitally, as a sequence of bits to be interpreted by a computer. By the end of the 20th century technological advances had made it feasible to distribute media content over a computer network instead of on physical objects, thus enabling the concept of digital media distribution. Many digital media distribution systems already exist, and their continued, and in many cases increasing, usage is an indicator for the high interest in their future enhancements and enriching. By looking at these digital media distribution systems, we have identified three main areas of possible improvement: network structure and coordination, transport of content over the network, and the encoding used for the content. In this thesis, our aim is to show that improvements in performance, efficiency and availability can be done in conjunction with improvements in software quality and reliability through the use of formal methods: mathematical approaches to reasoning about software so that we can prove its correctness, together with the desirable properties. We envision a complete media distribution system based on a distributed architecture, such as peer-to-peer networking, in which different parts of the system have been formally modelled and verified. Starting with the network itself, we show how it can be formally constructed and modularised in the Event-B formalism, such that we can separate the modelling of one node from the modelling of the network itself. We also show how the piece selection algorithm in the BitTorrent peer-to-peer transfer protocol can be adapted for on-demand media streaming, and how this can be modelled in Event-B. Furthermore, we show how modelling one peer in Event-B can give results similar to simulating an entire network of peers. Going further, we introduce a formal specification language for content transfer algorithms, and show that having such a language can make these algorithms easier to understand. We also show how generating Event-B code from this language can result in less complexity compared to creating the models from written specifications. We also consider the decoding part of a media distribution system by showing how video decoding can be done in parallel. This is based on formally defined dependencies between frames and blocks in a video sequence; we have shown that also this step can be performed in a way that is mathematically proven correct. Our modelling and proving in this thesis is, in its majority, tool-based. This provides a demonstration of the advance of formal methods as well as their increased reliability, and thus, advocates for their more wide-spread usage in the future.

Offline-tila web-sovelluksissa

Selainpohjaiset sovellukset ovat yleistyneet viimeisen kymmenen vuoden aikana. Samanaikaisesti ympäristö, jossa ihmiset käyttävät sovelluksia, on muuttunut. Nykyään sovelluksia käytetään yhä enenevissä määrin myös mobiililaitteilla, joissa verkkoyhteyden luotettavuus on huomattavasti heikompi kuin työpöytäympäristössä. Verkkoyhteyden toiminta on ehdoton edellytys web- sovelluksen toiminnalle. Kun verkkoyhteyttä ei ole, sovellusta ei useimmiten voi käyttää. Tilanne on käyttäjän kannalta sama myös, jos verkkoyhteyden laatu on hyvin heikko. Tämä uusi käyttöympäristö asettaa web-sovelluksen saavutettavuudelle haasteen, johon sovelluskehittäjien tulisi pystyä vastaamaan uusien teknologioiden avulla ja mahdollisesti sovelluksen arkkitehtuuria muuttamalla. Johdantona aiheeseen kerrotaan mitä hyötyjä offline-tilan tukemisesta on. Selainpohjaiset sovellukset kilpailevat jossain määrin mobiilialustojen natiivisovellusten kanssa. Web-sovelluksia on verrattu natiivisovelluksiin niiltä osin miten ne toimivat offline-tilassa. Pohjustuksena offline-tilan mahdollistavien teknologioiden arvioinnille esitellään Web-sovelluksen arkkitehtuuri yleisellä tasolla. Tässä tutkielmassa on esitelty muutamia offline-tilan asettamia vaatimuksia sovellukselle. Sovelluksen on kyettävä tunnistamaan, onko laitteella internet-yhteyttä. Yhteyden tilan tarkastukseen esitellään muutama vaihtoehto. Käyttäjän luoma tieto on myös tallennettava paikallisesti. Kun käyttäjä luo uutta sisältöä, se pitää tallentaa väliaikaisesti tai pysyvästi selaimeen. Ainakin osa sovelluksessa käsiteltävästä tiedosta pitäisi olla koko ajan saatavilla, käyttäjän internet-yhteyden tilasta riippumatta. Tähän tarkoitukseen selaimissa on nykyään käytettävissä muutamia erityyppisiä tietovarastoja. Kun selain on online-tilassa, sovelluksen tarvitsemat resurssit on tallennettava offline-tilaa varten. Tähän tarkoitukseen on luotu kaksi eri teknologiaa, HTML5 Application cache ja Service worker. Niiden avulla voi toteuttaa selaimen sisäisen välipalvelimen, joka vastaa sovelluksen tekemiin verkkopyyntöihin. Tutkielmassa esitellään näiden teknologioiden toimintaa teknisten määrittelydokumenttien ja verkkoartikkelien pohjalta. Mainittuja teknologoita vertaillaan keskenään toiminnallisten vaatimusten pohjalta. Tutkimuksen perusteella voidaan päätellä, että esitellyillä teknologioilla voidaan toteuttaa offline-tuki web-sovellukseen. Service worker osoittautuu paremmaksi vaihtoehdoksi kuin Application cache toiminnallisuudeltaan.

Remembering the War and Aggression: A Discourse Analysis of Japan’s State Apologies and Commemoration Speeches on August 15th 1995-2015

Memories of historical injustices affect contemporary politics from local to global level. In East Asia, questions of commemoration and historical responsibility have turned into international and domestic controversies. The main focus has been and still is in apologies conducted by Japanese prime ministers in regards to the war, aggression and colonialism during the era of Imperial Japan. Although it is granted that state apologies are not a crucial part of reconciliation, they can be analysed as a linked but separate process within the context of memory and international relations. The purpose of this study is to examine the discourses of history in Japanese prime ministers’ commemoration speeches on Memorial Ceremony for the War Dead from 1995 to 2015 in order to analyse how the Japanese government is reflecting on its past. In particular, attention is paid on what is being commemorated and how, whether it is the war and its victims or Japan’s post-war era of peace. As an apology is a reciprocal activity, responses from Japan’s most vocal former victims, South Korea and China, were also examined. Discourse analysis was used to identify and examine the different representations of the past. In addition, the apology statements of Japanese prime ministers were analysed in the Many to Many apology framework developed by Tavuchis (1991). Primary material consisted of 21 prime ministers’ speeches from the annual Memorial Ceremony for the War Dead on August 15th and from three apology statements made in 1995, 2005 and 2015. Further international context was primarily collected from newspaper articles of The New York Times and The Times throughout the examined period. It can be concluded from the findings that in the official Japanese remembrance of the past war from 1985’s annexation of Taiwan to the atomic bombings in 1945, both discourses that reinforce apology and remorse over Japan’s past aggressions and discourses that consciously avoid doing so are used. The commemoration speeches and apology statements consistently assert that Japan has acknowledged its past and expresses regret over the acts of aggression. At the same time, the speeches and statements strengthen the narrative that Japan was a victim of circumstances as well as turn the focus on post-war peace-making or on Japan’s own victimhood.