Editing GPSS (section)

==Description==
A GPSS simulation is written in an [[Assembly language|Assembly]]-style "block diagram language" with many different single-purpose commands ("Blocks") to control the flow of a ''Transaction'', statistics collection, and variables.

Simulations have ''Transaction'' entry points through the <code>GENERATE</code> command, such as a customer walking into a store. Then, actions are performed through claiming ''Facilities''/''Storage'' (like a cashier), waiting, saving statistics, etc. Finally, the simulated transaction exits the simulation through the <code>TERMINATE</code> command. Each command verb is referred to as a "control".

Blocks can be facility-oriented (such as machines in a job shop) or transaction-oriented (such parts of work-in-process, signals in electronic components or documents in a bureaucratic procedure). GPSS automatically keep track of statistics for display on a report.

Entities can be broadly classified in Resources, Computational entities and Statistical entities.<ref name="primer">{{cite book |author=Stanley Greenberg |title=GPSS Primer |publisher=Wiley-Interscience |year=1972 |isbn=0471324906 |location=New York}}</ref> Resources, like ''Facilities'' and ''Storages'' represent limited capacity resources.  Computational entities, like ''Ampervariables'' (variables), ''Functions'' and random generators are used to represent the state of Transactions or elements of their environment.  Statistical entities, like ''Queues'' or ''Tables'' (histograms) collect statistical information of interest.