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Global search and federated search might sound similar, and they often do similar things—helping people find information across different places. But they actually work in different ways and are used for different reasons. Understanding the difference between them can help you choose the right approach when building or using a search feature in a system.

1. Scope vs. Source

Aspect	Global Search	Federated Search
Definition	A search feature that allows users to search across all available data and content types within a single platform or system.	A search method that queries multiple distinct, often distributed, data sources (possibly on different systems) and aggregates the results.
Scope	Typically internal to one platform or ecosystem (e.g., all data in Synapse).	Cross-system or cross-repository search (e.g., searching Synapse, NIH databases, and GitHub simultaneously).
Goal	Convenience and comprehensiveness within one system.	Access and unify data that’s physically or logically separated.

2. Architecture

Feature	Global Search	Federated Search
Data indexing	Usually relies on a central index (e.g., ElasticSearch/OpenSearch) where all content is pre-crawled and indexed.	Each source maintains its own index; queries are sent to all sources in real time, and results are combined.
Performance	Faster, since all data is already indexed.	Slower, because queries are sent across multiple systems on-the-fly.
Result Ranking	More cohesive and consistent, often uses a single scoring model.	Harder to normalize ranking, since results come from heterogeneous sources.

3. Use Cases

Global Search

Searching within a large, feature-rich product (e.g., Synapse, Confluence).
Unified access across modules like datasets, users, files, and discussions.

Federated Search

Discovery across platforms (e.g., http://clinicaltrials.gov + PubMed + Synapse).
Search across government, academic, and private data silos.
Often used in federated biomedical infrastructures, library systems, or multi-institutional collaborations.

🧠 Example to Illustrate

Let’s say you're using Synapse:

A global search feature helps you search across projects, data, code, and wikis within Synapse.
A federated search tool might simultaneously query Synapse, PubMed, dbGaP, and Figshare, then return results from all those sources in a single view.

✅ Summary

	Global Search	Federated Search
Platform-bound	✅	❌
Cross-system	❌	✅
Real-time query	❌ (usually pre-indexed)	✅
Uniform ranking	✅	❌
Complexity	Moderate	High