With read caches, a data item must have been fetched from its residing location at least once in order for subsequent reads of the data item to realize a performance increase by virtue of being able to be fetched from the cache's (faster) intermediate storage rather than the data's residing location.
With write caches, a performance increase of writing a data item may be realized upon the first write of the data item by virtue of the data item immediately being stored in the cache's intermediate storage, deferring the transfer of the data item to its residing storage at a later stage or else occurring as a background process.
Subsequently, the supplier guarantees to the client that when a delete feature finishes its work, the data item will, indeed, be deleted from the buffer.
Any changes made by a writer will not be seen by other users of the database until the changes have been completed (or, in database terms: until the transaction has been committed.) When an MVCC database needs to update a piece of data, it will not overwrite the original data item with new data, but instead creates a newer version of the data item.
The concept of reference must not be confused with other values (keys or identifiers) that uniquely identify the data item, but give access to it only through a non-trivial lookup operation in some table data structure.
Primitive or group (record) data objects declared within the LINKAGE SECTION of a program are inherently pointer-based, where the only memory allocated within the program is space for the address of the data item (typically a single memory word).
Access to all the data in the system allows complex searches for data across all the data items managed by WinFS.
A WinFS item, along with the core data item, also contains information on how the data item is related to other data.
Links are physically stored using a link identifier, which specifies the name and intent of the relationship, such as type of or consists of. The link identifier is stored as an attribute of the data item.
An XML schema, defining the structure of the data items that will be stored in WinFS, must be supplied to the WinFS runtime beforehand.
WinFS models data using the data items, along with their relationships, extensions and rules governing its usage.
WinFS needs to understand the type and structure of the data items, so that the information stored in the data item can be made available to any application that requests it. This is done by the use of schemas.
And the type specifies the properties of the data item.