||This article may rely excessively on sources too closely associated with the subject, preventing the article from being verifiable and neutral. (July 2013)
Windows Azure SQL Database (formerly SQL Azure, SQL Server Data Services, and later SQL Services) is a cloud-based service from Microsoft offering data-storage capabilities (similar to Amazon Relational Database Service) as a part of the Azure Services Platform. Unlike similar cloud-based databases, SQL Azure allows users to make relational queries against stored data, which can either be structured or semi-structured, or even unstructured documents. SQL Azure features querying data, search, data analysis and data synchronization.
SQL Azure uses a special version of Microsoft SQL Server as its backend. It provides high availability by storing multiple copies of databases, elastic scale and rapid provisioning. It exposes a subset of the full SQL Server functionality, including only a subset of the data types — including string, numeric, date and boolean. It uses an XML-based format for data transfer. Like Microsoft SQL Server, SQL Azure uses T-SQL as the query language and Tabular Data Stream (TDS) as the protocol to access the service over internet. (The product does not provide a REST-based API to access the service over HTTP - Microsoft recommends using ADO.NET Data Services for this purpose.)