Microsoft Azure SQL Database (formerly SQL Azure, SQL Server Data Services, SQL Services, Windows Azure SQL Database) is a cloud-based service from Microsoft offering data-storage capabilities. The aim is for users to just communicate with a T-SQL endpoint rather than managing database storage, files, and high availability. In this regard, it is a similar offering to Amazon Relational Database Service. Early versions operated as key-value pair tables accessed via a REST-based API, and offering only a subset of the data types offered by the Microsoft SQL Server on-premises product. Using these versions was not similar to using the SQL Server database engine and led to relatively low adoption rates. Current versions of Azure SQL Database share a common code base with Microsoft SQL Server. This database engine allows users to make relational queries against stored data, which can either be structured or semi-structured, and unstructured documents. SQL Database features querying data, search, data analysis and data synchronization. High availability is provided by storing multiple copies of databases, business continuity and disaster recovery with backups and geo-replication, elastic scale and rapid provisioning. It has built-in data protection and security features. Like Microsoft SQL Server, SQL Database uses T-SQL as the query language and Tabular Data Stream (TDS) as the protocol to access the service over the Internet. (The product no longer provides a REST-based API to access the service over HTTP - Microsoft recommends using ADO.NET Data Services for this purpose.)