Data Store vs. Central Buffer

Central Buffers and Data Stores are special types of Object Nodes.  A Central Buffer “provides a store for object tokens outside of pins and parameter nodes” on an activity diagram.  The Data Store is similar in that it also stores object tokens, but differs from the Central Buffer in that it provides a copy of the token.  Central Buffers and Data Stores are represented as rectangles situated between action pins and include either «centralBuffer» or «datastore» on the rectangle.

Friendenthal states that a Central Buffer is needed “when there are multiple producers and consumers of a single buffered stream of tokens at the same time.”  For example, there may be multiple streams of packetized data entering a Central Buffer; that packetized data may be routed to different devices on the network (i.e., attached to the Central Buffer).

If the exact same stored object token is required by multiple actions, then a Data Store should be used to store the object tokens.  For example, a video splitter connected to two televisions must provide the same video stream to each television.  If a token representing an object already exists in the Data Store enters the Data Store, then the old object token is re-written by the new one.

Example of a Data Store and a Central Buffer

Central buffers and Data Stores belong to an activity, and as such, object tokens kept by the Central Buffer or the Data Store only exist while their parent activity is executing.

Reference:

Friedenthal, S., Moore, A., & Steiner, R. (2012) A Practical Guide to SysML. Waltham, MA: Morgan Kaufmann. pg. 219, 580.