SQL Azure

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 those of Amazon S3 and 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.)