# What is Data Publisher? and What is Subscriber? **URL:** \ **Category:** openHistorian\ **Created:** [October 24, 2019, 7:01am UTC](http://discussions.gridprotectionalliance.org/t/what-is-data-publisher-and-what-is-subscriber/589 "2019-10-24T07:01:59Z")\ **Posts on this page:** 1\ **Showing post:** 2
**Author:** ![StephenCWills](http://discussions.gridprotectionalliance.org/user_avatar/discussions.gridprotectionalliance.org/stephencwills/32/20_2.png) [@StephenCWills](http://discussions.gridprotectionalliance.org/u/StephenCWills)\ **Post date:** [October 25, 2019, 7:14pm UTC](http://discussions.gridprotectionalliance.org/t/what-is-data-publisher-and-what-is-subscriber/589/2 "2019-10-25T19:14:26Z")
Hello ankitshah-it, I’ll do my best to clarify these points. 1. Fundamentally, nearly every piece of functionality in the openHistorian is either an **input adapter** , **action adapter** , or **output adapter**. Every device in the Device table is converted into an input adapter, the type of which is determined by the `Protocol` field. You can see the mappings between protocols and their respective code modules by looking at the Protocol table. Specifically, the [DataSubscriber](https://github.com/GridProtectionAlliance/gsf/blob/master/Source/Libraries/GSF.TimeSeries/Transport/DataSubscriber.cs#L72) class itself is the input adapter for a GEP data subscriber. 2. No, subscriber is a GEP Data Subscriber just like the one used in DataSubscriberTest. 3. Take a look at the following explanation to better understand Receive Internal Metadata and receive External Metadata. [Forwarding measurements limitation?](https://gridbits.gridprotectionalliance.org/t/forwarding-measurements-limitation/548/4) 4. `Adder` and `Multiplier` define the linear adjustments used when determining the `AdjustedValue` of the measurement: `AdjustedValue = Value * Multiplier + Adder`. Thanks, Stephen --- _[View the full topic](http://discussions.gridprotectionalliance.org/t/what-is-data-publisher-and-what-is-subscriber/589)._