PS: Use the existing MaD rows to model file reads as flow sources.

powershell/ql/lib/semmle/code/powershell/dataflow/flowsources/FlowSources.qll

@@ -2,6 +2,7 @@
 private import semmle.code.powershell.dataflow.internal.DataFlowPublic as DataFlow
 import semmle.code.powershell.dataflow.flowsources.Remote
 import semmle.code.powershell.dataflow.flowsources.Local
+import semmle.code.powershell.dataflow.flowsources.Stored
 import semmle.code.powershell.frameworks.data.internal.ApiGraphModels
 
 /**

powershell/ql/lib/semmle/code/powershell/dataflow/flowsources/Stored.qll

@@ -0,0 +1,35 @@
+/**
+ * Provides classes representing sources of stored data.
+ */
+
+import powershell
+private import FlowSources
+
+/** A data flow source of stored user input. */
+abstract class StoredFlowSource extends SourceNode {
+  override string getThreatModel() { result = "local" }
+}
+
+/**
+ * A node with input from a database.
+ */
+abstract class DatabaseInputSource extends StoredFlowSource {
+  override string getThreatModel() { result = "database" }
+
+  override string getSourceType() { result = "database input" }
+}
+
+private class ExternalDatabaseInputSource extends DatabaseInputSource {
+  ExternalDatabaseInputSource() { this = ModelOutput::getASourceNode("database", _).asSource() }
+}
+
+/** A file stream source is considered a stored flow source. */
+abstract class FileStreamStoredFlowSource extends StoredFlowSource {
+  override string getThreatModel() { result = "file" }
+
+  override string getSourceType() { result = "file stream" }
+}
+
+private class ExternalFileStreamStoredFlowSource extends FileStreamStoredFlowSource {
+  ExternalFileStreamStoredFlowSource() { this = ModelOutput::getASourceNode("file", _).asSource() }
+}