diff --git a/src/EquationGen.js b/src/EquationGen.js
index 52be92f5..975e548e 100644
--- a/src/EquationGen.js
+++ b/src/EquationGen.js
@@ -330,10 +330,10 @@ export default class EquationGen extends ModelReader {
     // If direct data exists for this variable, copy it from the workbook into one or more lookups.
     let result = []
     if (this.mode === 'init-lookups') {
-      let { tag, sheetName, timeRowOrCol, startCell } = this.var.directDataArgs
-      let workbook = this.directData.get(tag)
+      let { file, tab, timeRowOrCol, startCell } = this.var.directDataArgs
+      let workbook = this.directData.get(file)
       if (workbook) {
-        let sheet = workbook.Sheets[sheetName]
+        let sheet = workbook.Sheets[tab]
         if (sheet) {
           let indexNum = 0
           if (!R.isEmpty(this.var.subscripts)) {
@@ -344,10 +344,10 @@ export default class EquationGen extends ModelReader {
           }
           result.push(this.generateDirectDataLookup(sheet, timeRowOrCol, startCell, indexNum))
         } else {
-          throw new Error(`ERROR: Direct data worksheet ${sheetName} tagged ${tag} not found`)
+          throw new Error(`ERROR: Direct data worksheet ${tab} tagged ${file} not found`)
         }
       } else {
-        throw new Error(`ERROR: Direct data workbook tagged ${tag} not found`)
+        throw new Error(`ERROR: Direct data workbook tagged ${file} not found`)
       }
     }
     return result
diff --git a/src/EquationReader.js b/src/EquationReader.js
index 9c4cf204..b102e835 100644
--- a/src/EquationReader.js
+++ b/src/EquationReader.js
@@ -127,13 +127,17 @@ export default class EquationReader extends ModelReader {
       this.expandDelayFunction(fn, args)
     } else if (fn === '_GET_DIRECT_DATA') {
       // Extract string constant arguments into an object used in code generation.
+      // For Excel files, the file argument names an indirect "?" file tag from the model settings.
+      // For CSV files, it gives a relative pathname in the model directory.
+      // For Excel files, the tab argument names an Excel worksheet.
+      // For CSV files, it gives the delimiter character.
       let args = R.map(
         arg => matchRegex(arg, /'(.*)'/),
         R.map(expr => expr.getText(), ctx.expr())
       )
       this.var.directDataArgs = {
-        tag: args[0],
-        sheetName: args[1],
+        file: args[0],
+        tab: args[1],
         timeRowOrCol: args[2],
         startCell: args[3]
       }
diff --git a/src/sde-generate.js b/src/sde-generate.js
index be96aa73..9f6d8271 100644
--- a/src/sde-generate.js
+++ b/src/sde-generate.js
@@ -107,12 +107,12 @@ export let generate = async (model, opts) => {
       extData = new Map([...extData, ...data])
     }
   }
-  // Attach Excel workbook data to directData entries by tag name.
+  // Attach Excel workbook data to directData entries by file name.
   let directData = new Map()
   if (spec.directData) {
-    for (let [tag, xlsxFilename] of Object.entries(spec.directData)) {
+    for (let [file, xlsxFilename] of Object.entries(spec.directData)) {
       let pathname = path.join(modelDirname, xlsxFilename)
-      directData.set(tag, readXlsx(pathname))
+      directData.set(file, readXlsx(pathname))
     }
   }
   // Produce a runnable model with the "genc" and "preprocess" options.