Browsing Elements
By its nature, COM's structured storage separates applications from the exact layout of information within a given file. Every element of information in that file is access using functions and interfaces implemented by COM. Because this implementation is central, a file generated by some application using this structure can be browsed by some other piece of code, such as a system shell. In other words, any piece of code in the system can use COM to browse the entire hierarchy of elements within any structured file simply by navigating with the IStorage interface functions which provide directory-like services. If that piece of code also knows the format and the meaning of a specific stream that has a certain name, it could also open that stream and make use of the information in it, without having to run the application that wrote the file.
This is a powerful enabling technology for operating system shells that want to provide rich query tools to help end users look for information on their computer or even on a network. To make it really happen requires standards for certain stream names and the format of those streams such that the system shell can open the stream and execute queries against that information. For example, consider what is possible if all applications created a stream called "Summary Information" underneath the root storage element of the file. In this stream the application would write information such as the author of the document, the create/modify/last saved time stamps, title, subject, keywords, comments, a thumbnail sketch of the first page, and so forth. Using this information the system shell could find any documents that a certain user wrote before a certain date or those that contained subject matter matched against a few keywords. Once those documents are found, the shell can then extract the title of the document along with the thumbnail sketch and give the user a very engaging display of the search results.
This all being said, the general the actual utility of this capability is perhaps significantly less than what one might first imagine. Suppose, for example, that I have a structured storage that contains some word processing document whose semantics and persistent representation I am unaware of, but which contains some number of contained objects, perhaps the figures in the document, that I can identify by their being stored and tagged in contained sub-storages. One might naively think that it would be reasonable to be able to walk in and browse the figures from some system-provided generic browsing utility. This would indeed work from a technical point of view; however, it is unlikely to be useable from a user interface perspective.
The document may contain hundreds of figures, for example, that the user created and thinks about not with a name, not with a number, but only in the relationship of a particular figure to the rest of the document's information. With what user interface could one reasonably present this list of objects to the user other than as some add-hoc and arbitrarily-ordered sequence? There is, for example, no name associated with each object that one could use to leverage a file system directory-browsing user interface design. In general, the content of a document can only reasonably be presented to a human being using a tool that understands the semantics of the document content, and thus can show all of the information therein in its appropriate context.