COM Structured Storage

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COM Structured Storage (variously also known as COM structured storage or OLE structured storage) is a technology developed by Microsoft as part of its Windows operating system for storing hierarchical data within a single file. Strictly speaking, the term structured storage refers to a set of COM interfaces that a conforming implementation must provide, and not to a specific implementation, nor to a specific file format (in fact, a structured storage implementation need not store its data in a file at all). In addition to providing a hierarchical structure for data, structured storage may also provide a limited form of transactional support for data access. Microsoft provides an implementation that supports transactions, as well as one that does not (called simple-mode storage, the latter implementation is limited in other ways as well, although it performs better).

Structured storage is widely used in Microsoft Office applications, although newer releases (starting with Office 2007) use the XML-based Office Open XML by default. It is also an important part of both COM and the related Object Linking and Embedding (OLE) technologies. Other notable applications of structured storage include SQL Server, the Windows shell, and many third-party CAD programs.