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Lens Execution Environment (LEE)

The LEE (Lens Execution Environment) is the service that executes Lens logic on p(ePI) using patient contextual data to produce the final f(ePI).

Purpose​

LEE provides a sandboxed runtime environment for executing Lens JavaScript code safely and efficiently.

Execution Process​

  1. Receives request from Focusing Manager
  2. Loads Lens code from FHIR Library resource
  3. Decodes Base64 content, then interprets as UTF-8 JavaScript
  4. Prepares inputs: p(ePI), IPS, PV
  5. Executes lens in isolated context
  6. Applies modifications to generate f(ePI)
  7. Returns result to Focusing Manager

Helper Methods​

LEE provides APIs for Lenses to use:

modifyCSSClass()​

Applies attention detail modifications:

// Function signature
modifyCSSClass(elementClass, action)

// Examples
modifyCSSClass("pregnancy-warning", "highlight");
modifyCSSClass("pediatric-info", "collapse");
modifyCSSClass("general-info", "standard");

addNewContent()​

Inserts supplementary HTML:

// Function signature
addNewContent(targetLocation, htmlContent)

// Examples
addNewContent("section-4", '<a href="/sm/guide">Read more</a>');
addNewContent("warnings", '<img src="/icons/warning.png" />');
addNewContent("dosing", '<video src="/videos/howto.mp4"></video>');

Execution Modes​

Client-Side Focusing​

  • LEE runs in patient's browser/app
  • Uses local patient data (IPS/PV)
  • Privacy-preserving (data never leaves device)
  • Requires lightweight Lenses

Server-Side Focusing​

  • LEE runs on FOSPS servers
  • Receives patient data from secure sources
  • Must scale for concurrent users
  • Enables more complex lenses

Security & Isolation​

  • Sandboxed execution: Lenses cannot access system resources
  • Time limits: Prevent infinite loops
  • Memory limits: Prevent resource exhaustion
  • API restrictions: Only approved helper methods available

Architecture Position​

Located in the Service Layer of FOSPS.

Integration​