An industrial data indexing system facilitates discovery and indexing of plant-wide data residing on multiple different data platforms. The indexing system automatically inventories industrial devices and other data sources located throughout a plant, and identifies available data items on each data source. The indexing system indexes the discovered data items in a federated data model that can subsequently be searched to locate data items or tags of interest. The federated data model records references to data items found on different types of data sources, including but not limited to industrial controller programs, human-machine interface applications, data historians, device documentation stores, inventory tracking systems, and other such data sources. The search system also caches selected portions of the data model to a user's personal device to allow these potions of the model to be accessed locally on the user's device without being online with the higher level indexing system.