When you are creating new software today, more often than not you will use API’s. Users choosing between different API’s would probably look at functionality but also accessibility and ease of use. It would therefore seem motivated for API providers to create usable and accessible API’s.This thesis is about the things that make an API more usable, and then those things are used in practice to increase the usability of CloudMe’s API. CloudMe’s core API is documented to increase usability and a wrapper for the API is developed to allow people more ways to use CloudMe’s service. The APIwrapper is created in Java and was developed thoroughly with regards to usability.

Transport Layer Security (TLS) is a secure communication protocol between a client and a server over a network. The TLS protocol provides the two endpoints with confidentiality through symmetric encryption, endpoint authentication using public-key cryptography, and data integrity using a MAC. However, studies show that security vulnerabilities within TLS connections are often caused by developers misusing TLS library APIs. We measure the usability of four TLS libraries by performing a developer user study. Participants were given code that connects to google.com through HTTP, and tasked with using a TLS library to change the code so that it connects securely to Google through HTTPS. Our results help show what makes a library usable and what problems arise for developers using these TLS libraries. We found that the main way to ensure a TLS library is usable is to focus on having clear documentation. From our results, we provide suggestions on how to create usable documentation.

Användbarheten hos ett API kan vara en viktig faktor för en slutanvändares produktivitet, eller framgången en mjukvaruprodukt. Det finns ingen enskild definition av, eller metod för att uppnå användbarhet. Många riktlinjer kan vara teoretiska och svårapplicerade. Detta arbete sammanfattar definitioner av och utvärderingsmetoder för användbarhet. En av dessa metoder anpassas och används för en formativ utvärdering som del av utvecklingsprocessen av ett nytt API för röstchatt i webben. API:et specificeras och implementeras i en första version som utvärderas med testanvändare för att hitta användbarhetsproblem. Förbättringsförslag för API:ets vidareutveckling ges baserat på funna problem. Avslutningsvis diskuteras utvärderingsmetoderna utifrån resurserna som krävs för genomförande. / The usability of an API can be an important factor for the productivity of end users, or the success of a software product. There is no single definition of, or method to achieve, usability. Many guidelines can be theoretical and difficult to apply. This paper summarises usability definitions and evaluation methods. One of these methods is adapted and used for a formative evaluation as part of the development process of a new API for web based voice chat. The API is specified and implemented in a first version which is evaluated with test users to find usability problems. Improvement proposals for the further development of the API are given based on found problems. In closing, the evaluation methods are discussed based on the resources required for execution.

In today’s computer environments the systems are getting bigger and more complex for each day that passes by. The motivating factor for this is that the customer wants to achieve more and more with their computer systems than before. The only way to really solve this task is to use even more APIs (Application program interfaces) in their systems.     When using more APIs in a system, there is a chance that the specific system provides the same type of API twice, which of course, is a waste of storage and resources. In addition, the more APIs a system contains, the bigger the risk is for mismanagement of these APIs. In the worst case, this can result in security breaches or data leaks.  This thesis investigates specific APIs provided for a customer of Sigma IT Consulting. The aim is to evaluate and organize the APIs according to their usability criteria. The main focus of the evaluation is the available documentation which will be evaluated by a questionnaire survey distributed to senior software developers at Sigma IT Consulting in Växjö. Conclusions will then be drawn depending on the result from the survey, and we can then see if Azure API management (which is a service to make a system more user – friendly) is accurate in its way of organizing with the API usability as the main focus! Unfortunately, Azure API management did not have any possibility what so ever to customize the API placement in a system, and the only way the APIs are organized is in alphabetical order. Therefore, a prototype with even more sorting functionality than Azure API management will also be presented in this thesis.

Les systèmes logiciels dépendent de plus en plus des librairies et des frameworks logiciels. Les programmeurs réutilisent les fonctionnalités offertes par ces librairies à travers une interface de programmation (API). Par conséquent, ils doivent faire face à la complexité des APIs nécessaires pour accomplir leurs tâches, tout en surmontant l’absence de directive sur l’utilisation de ces API dans leur documentation. Dans cette thèse, nous proposons une approche holistique qui cible le problème de réutilisation des librairies, à trois niveaux. En premier lieu, nous nous sommes intéressés à la réutilisation d’une seule méthode d’une API. À ce niveau, nous proposons d’identifier les contraintes d’utilisation liées aux paramètres de la méthode, en analysant uniquement le code source de la librairie. Nous avons appliqué plusieurs analyses de programme pour détecter quatre types de contraintes d’utilisation considérées critiques. Dans un deuxième temps, nous changeons l’échelle pour nous focaliser sur l’inférence des patrons d’utilisation d’une API. Ces patrons sont utiles pour aider les développeurs à apprendre les façons courantes d’utiliser des méthodes complémentaires de l’API. Nous proposons d’abord une technique basée sur l’analyse des programmes clients de l’API. Cette technique permet l’inférence de patrons multi-niveaux. Ces derniers présentent des relations de co-utilisation entre les méthodes de l’API à travers des scénarios d’utilisation entremêlés. Ensuite, nous proposons une technique basée uniquement sur l’analyse du code de la librairie, pour surmonter la contrainte de l’existence des programmes clients de l‘API. Cette technique infère les patrons par analyse des relations structurelles et sémantiques entre les méthodes. Finalement, nous proposons une technique coopérative pour l’inférence des patrons d’utilisation. Cette technique est axée sur la combinaison des heuristiques basées respectivement sur les clients et sur le code de la librairie. Cette combinaison permet de profiter à la fois de la précision des techniques basées sur les clients et de la généralisabilité des techniques basées sur les librairies. Pour la dernière contribution de notre thèse, nous visons un plus haut niveau de réutilisation des librairies. Nous présentons une nouvelle approche, pour identifier automatiquement les patrons d’utilisation de plusieurs librairies, couramment utilisées ensemble, et généralement développées par différentes tierces parties. Ces patrons permettent de découvrir les possibilités de réutilisation de plusieurs librairies pour réaliser diverses fonctionnalités du projets. / Software systems increasingly depend on external library and frameworks. Software developers need to reuse functionalities provided by these libraries through their Application Programming Interfaces (APIs). Hence, software developers have to cope with the complexity of existing APIs needed to accomplish their work, and overcome the lack of usage directive in the API documentation. In this thesis, we propose a holistic approach that deals with the library usability problem at three levels of granularity. In the first step, we focus on the method level. We propose to identify usage constraints related to method parameters, by analyzing only the library source code. We applied program analysis strategies to detect four critical usage constraint types. At the second step, we change the scale to focus on API usage pattern mining in order to help developers to better learn common ways to use the API complementary methods. We first propose a client-based technique for mining multilevel API usage patterns to exhibit the co-usage relationships between API methods across interfering usage scenarios. Then, we proposed a library-based technique to overcome the strong constraint of client programs’ selection. Our technique infers API usage patterns through the analysis of structural and semantic relationships between API methods. Finally, we proposed a cooperative usage pattern mining technique that combines client-based and library-based usage pattern mining. Our technique takes advantage at the same time from the precision of the client-based technique and from the generalizability of the library-based technique. As a last contribution of this thesis, we target a higher level of library usability. We present a novel approach, to automatically identify third-party library usage patterns, of libraries that are commonly used together. This aims to help developers to discover reuse opportunities, and pick complementary libraries that may be relevant for their projects.