Team Foundation Server - Architecture

Architecture

Team Foundation Server works in a three-tier architecture: the client tier, the application tier and the data tier. The client tier is used for creating and managing projects and accessing the items that are stored and managed for a project. TFS does not include any user interface for this tier, rather it exposes web services which client applications can use to integrate TFS functionality with themselves. These web services are used by applications like Visual Studio Team System to use TFS as data storage back end or dedicated TFS management applications like the included Team Foundation Client. The web services are in the application layer. The application layer also includes a web portal and a document repository facilitated by Windows SharePoint Services. The web portal, called the Team Project Portal, acts as the central point of communication for projects managed by TFS. The document repository is used for both project items and the revisions tracked, as well as for aggregated data and generated reports. The data layer, essentially an SQL Server 2005 Standard Edition installation, provides the persistent data storage services for the document repository. The data tier and application tier can exist on different physical or virtual servers as well, provided they are running Windows Server 2003 or later. The data tier is not exposed to the client tier; only the application tier is.

Most activity in Team Foundation Server revolves around a "work item". A work item is a single unit of work which needs to be completed. In many respects it is similar to a "bug" item in bug tracking systems such as Bugzilla, in that it has fields to define Area, Iteration, Assignee, Reported By, a history, file attachments, and any number of other attributes. Work items themselves can be of several different types, such as a Bug, a Task, a Quality of Service Assessment, a Scenario, and so forth. The framework chosen for any given project in a Team Foundation Server defines what types of work items are available and what attributes each type of work item contains. These items are internally stored in XML format, and their schema can be customized to add other attributes to different items, or create new items on a per-project basis. Each work item has associated control policies which control who is allowed to access and/or change the items. It also includes notification and logging capabilities to log all the creation, access or change events (controlled by policies) and optionally notify certain users when certain events occur.

Any given Team Foundation Server contains one or more Team Projects, which consists of Visual Studio solutions, configuration files for Team Build and Team Load Test Agents, and a single SharePoint repository containing the pertinent documents for the project. A team project contains the user defined work items, source branches, and reports that are to be managed by TFS. TFS provides capabilities for managing these projects. When creating a project, a software development framework must be chosen, and cannot be changed afterwards. TFS includes several templates for the most common ones, including agile and formal methodologies. Choosing the framework populates the project with predefined items such as project roles and permissions, as well as other documents like project roadmap, document templates, and report definitions. These items can be then linked to work items as well. The status of certain elements of the project can be set to automatically update as work items are updated. TFS can integrate with Microsoft Excel for the creation and tracking of project items. The status of the items can be created and edited in Excel and the resulting spreadsheet document can be submitted to TFS, which will import the data into its project management feature. It can also integrate with Microsoft Project as the project management front end. The project items can also be exported as Excel documents for further analysis of the data.

TFS does not natively include a UI for performing these tasks. The capabilities are exposed via web services, which are then used by client applications like Visual Studio Team System IDE. However, TFS does include a Team Foundation Client (TFC) application which can be used to perform these tasks outside of the VSTS IDE. TFC also operates by invoking the same web services. TFS exposes a client API that can be used by client applications to access the functionality; the API itself manages proxies to communicate with the web services as well as client side caching to reduce latency. The WSDL descriptions of the web services are also provided, in case an application wants to directly call the web services. Visual Studio Team System Web Access, available as an add-on, also addresses this.