Technical Sessions

Web applications are fundamentally reactive. Code in a web page runs in reaction to events, which are triggered either by external stimuli or by other events. The DOM, which specifies these behaviors, is therefore central to the behavior of web applications. We define the first formal model of event behavior in the DOM, with high fidelity to the DOM specification. Our model is concise and executable, and can therefore be used for testing and verification. We have applied it in several settings: to establish some intended meta-properties of the DOM, as an oracle for testing the behavior of browsers (where it found real errors), to demonstrate unwanted interactions between extensions and validate corrections to them, and to examine the impact of a web sandbox. The model composes easily with models of other web components, as a step toward full formal modeling of the web.

Mapping user profiles across social network sites enables sharing and interactions between social networks, which enriches the social networking experience. Manual mapping for user profiles is a time consuming and tedious task. In addition profile mapping algorithms are inaccurate and are usually based on simple name or email string matching. In this paper, we propose a Game With A Purpose (GWAP) approach to solve the profile mapping problem. The proposed approach leverages the game appeal and social community to generate the profile mappings. We designed and implemented an online social networking game (GameMapping), the game is fun and is based on human verification. The game presents the players with some profiles information, and uses human computation and knowledge about the information being presented to map similar user profiles. The game was modeled using incomplete information game theory, and a proof of sequential equilibrium was provided. To test the effectiveness of the mapping technique and detection strategies, the game was implemented and deployed on Facebook, MySpace and Twitter and the experiments were performed on the real data collected from users playing the game.

Platform-as-a-service (PaaS) systems, such as Google App Engine (GAE), simplify web application development and cloud deployment by providing developers with complete software stacks: runtime systems and scalable services accessible from well-defined APIs. Extant PaaS offerings are designed and specialized to support large numbers of concurrently executing web applications (multi-tier programs that encapsulate and integrate business logic, user interface, and data persistence). To enable this, PaaS systems impose a programming model that places limits on available library support, execution duration, data access, and data persistence. Although successful and scalable for web services, such support is not as amenable to online analytical processing (OLAP), which have variable resource requirements and require greater flexibility for ad-hoc query and data analysis. OLAP of web applications is key to understanding how programs are used in live settings.

In this work, we empirically evaluate OLAP support in the GAE public cloud, discuss its benefits, and limitations. We then present an alternate approach, which combines the scale of GAE with the flexibility of customizable offline data analytics. To enable this, we build upon and extend the AppScale PaaS – an open source private cloud platform that is API-compatible with GAE. Our approach couples GAE and AppScale to provide a hybrid cloud that transparently shares data between public and private platforms, and decouples public application execution from private analytics over the same datasets. Our extensions to AppScale eliminate the restrictions GAE imposes and integrates popular data analytic programming models to provide a framework for complex analytics, testing, and debugging of live GAE applications with low overhead and cost.

Partitioning data over multiple storage servers is an attractive way to increase throughput for web-like workloads. However, there is often no one partitioning that yields good performance for all queries, and it can be challenging for the web developer to determine how best to execute queries over partitioned data.

This paper presents DIXIE, a SQL query planner, optimizer, and executor for databases horizontally partitioned over multiple servers. DIXIE focuses on increasing inter-query parallel speedup by involving as few servers as possible in each query. One way it does this is by supporting tables with multiple copies partitioned on different columns, in order to expand the set of queries that can be satisified from a single server. DIXIE automatically transforms SQL queries to execute over a partitioned database, using a cost model and plan generator that exploit multiple table copies.

We evaluate DIXIE on a database and query stream taken from Wikipedia, partitioned across ten MySQL servers. By adding one copy of a 13 MB table and using DIXIE’s query optimizer, we achieve a throughput improvement of 3.2X over a single optimized partitioning of each table and 8.5X over the same data on a single server. On specific queries DIXIE with table copies increases throughput linearly with the number of servers, while the best single-table-copy partitioning achieves little scaling. For a large class of joins, which traditional wisdom suggests requires tables partitioned on the join keys, DIXIE can find higher-performance plans using other partitionings.

Traditional web-based client-server application development has been accomplished in two separate pieces: the frontend portion which runs on the client machine has been written in HTML and JavaScript; and the backend portion which runs on the server machine has been written in PHP, ASP.net, or some other “server-side” language which typically interfaces to a database. The skill sets required for these two pieces are different.

In this paper, I demonstrate a new methodology for web-based client-server application development, in which a simulated server is built into the browser environment to run the backend code. This allows the frontend to issue requests to the backend, and the developer to step, using a debugger, directly from frontend code into backend code, and to debug and test both the frontend and backend portions. Once working, that backend code is moved to a real server. Since the application-specific code has been tested in the simulated environment, it is unlikely that bugs will be encountered at the server that did not exist in the simulated environment.

I have implemented this methodology and used it for development of a live application. All of the code is open source.

Twitter has become a persistent part of our digital lives, connecting us not only to our individual audiences but also to an entire landscape of applications built for the web. While much has been done to support the Twitter ecosystem outside of Twitter, little has been done within Twitter to power those same applications. This work introduces a service called Aperator, which supports application-specific actionable commands through tweets. This ability creates several interesting opportunities for both end-users and application developers building on the Twitter platform. For example, the actionable command capability allows a link that a Twitter user shares with his followers to be directly added to any of the user’s connected link sharing networks, such as Delicious or Read it Later. The client side of this system has a console for end-users to sign up and provide their login credentials for various web services that our system supports: Delicious, Foursquare, Read it Later, Foursquare etc. The system’s backend has two cron jobs that run every minute to: (a) retrieve and parse tweets from a specific twitter account and store them in a command form in a MySQL database, and (b) execute the unexecuted commands found in the users tweets. This paper describes the concept, implementation, and results from an experimental study of this new application.