Introduction to Data Management

Glossary
15873 Tandem Computers Incorporated Glossary-15
Transaction. A group of computer operations that reflect a particular commercial
interaction. These operations, including the entry of data about the interaction, the
processing of that data, and the resulting change in the database, provide a computer
model of the real events making up the transaction. A transaction might insert an
airline flight reservation record or transfer money from one bank account record to
another. Using TMF in the PATHWAY environment, the software ensures database
consistency by guaranteeing that no transaction is considered complete until all
operations within the transaction are complete. For example, if a banking transaction
includes two operations--one debiting one account and a second crediting another
account--neither operation is desirable if the other is not complete. So, the transaction
would include sending the interprocess request message from the requester to the
server, then doing both the debiting and crediting operations on the database, and
then sending the interprocess reply message back to the requester to confirm
transaction completion. Changes to the database are not final until both operations
are completed. See also TMF transaction.
Transaction backout. See Backout.
Transaction Monitoring Facility. See TMF.
Unstructured file. A file that is essentially a large byte array that is not inherently
divided into records and fields. This kind of file normally contains text produced by
text editors (such as source code or documentation), or object code produced by
compilers. The organization of an unstructured file in terms of record length and
location is managed by the application program that uses the file, and that accesses
the data in terms of an offset from the first byte in the file.
User. See End user.
Video attribute. A property of a screen element that determines the visual appearance
of the screen-image locations occupied by the element. On screens generated by
PATHMAKER, for instance, an element can be bright or dim, steady or blinking, light-
on-dark or reversed, underlined or not, visible or hidden.
View. In NonStop SQL, a table that has a logical definition but no physical existence.
A view is derived by projecting a subset of the columns and/or selecting a subset of
the rows from one or more tables or other views.
VIEWPOINT. A software tool for interacting with multiple Tandem products, including
PATHCOM, allowing an operator to easily control an integrated Tandem system
through a single interface.
Virtual memory paging. The movement of code and data from disk into main memory,
or vice-versa. Normally, active portions of code or data reside in main memory but
inactive portions remain in virtual memory on disk until they are needed. Virtual
memory effectively extends main memory to disk. Virtual memory for code is the file
that contains your program, while virtual memory for data is the temporary disk
storage allocated at process creation.