initial SDTH ReSpec skeleton

Author: DanSmith

.github/workflows/ci-push-master.yml

@@ -77,3 +77,4 @@ jobs:
     - name: Sync S3 dev bucket
       run: |
         aws s3 sync sdtl-outputs-${{env.SHORT_SHA}}\sphinx\build\dirhtml s3://docs.ddialliance.org/SDTL/dev/model
+        aws s3 sync SDTH\doc\ s3://docs.ddialliance.org/SDTL/dev/SDTH

SDTH/doc/assets/ddi.svg

@@ -0,0 +1,51 @@
+
+classDiagram
+  
+  class Program["sdth:Program"] {
+    rdfs:label
+  }
+  class ProgramStep["sdth:ProgramStep"] {
+    rdfs:label
+    sdth:hasSourceCode
+    sdth:hasSDTL
+  }
+  class VariableInstance["sdth:VariableInstance"] {
+    rdfs:label
+    sdth:hasName    
+  }
+  class DataframeInstance["sdth:DataframeInstance"] {
+    rdfs:label
+    sdth:hasName
+  }
+
+class FileInstance["sdth:FileInstance"] {
+    rdfs:label
+    sdth:hasName
+  }
+
+  
+  ProgramStep <-- Program : sdthhasProgramStep
+  ProgramStep <-- ProgramStep : sdth_hasProgramStep
+
+  ProgramStep --> VariableInstance : sdth_usesVariable
+  ProgramStep --> VariableInstance : sdth_assignsVariable
+  ProgramStep --> DataframeInstance : sdth_consumesDataframe
+  ProgramStep --> DataframeInstance : sdth_producesDataframe
+
+  ProgramStep --> FileInstance : sdth_loadsFile
+  ProgramStep --> FileInstance : sdth_savesFile
+
+
+  DataframeInstance --> VariableInstance : sdth_hasVariableInstance
+  FileInstance --> VariableInstance : sdth_hasVariableInstance
+
+
+  DataframeInstance --> DataframeInstance : sdth_derivedFrom
+  DataframeInstance --> DataframeInstance : sdth_elaborationOf
+
+  FileInstance --> FileInstance : sdth_derivedFrom
+  FileInstance --> FileInstance : sdth_elaborationOf
+  VariableInstance --> VariableInstance : sdth_derivedFrom
+  VariableInstance --> VariableInstance : sdth_elaborationOf
+
+```

SDTH/doc/assets/sdth_diagram.mmd

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+# Background and Motivation
+
+SDTH was created to provide a simple way to describe the key features of a data transformation script.  SDTH answers questions such as: “Which variables affected variable X?” and “Which variables were affected by file Y?”  
+
+SDTH focuses on how data entities (variables, dataframes, and files) are related to each other and to the steps in a program that change them.  
+    

SDTH/doc/assets/sdth_diagram.png

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+# Examples

SDTH/doc/content/background.markdown

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+# Introduction
+
+## SDTH and PROV
+
+## Instances of data objects
+
+SDTH requires a change in the way that one thinks about a computer program.  We usually think of variables and dataframes as containers into which we put digital representations of numbers, text, or logical values.  As the program is executed, the values assigned to a variable or dataframe change, but its identity remains the same.  We may think of these sets of values as states of the variable/dataframe.  Since variables and dataframes can change, they do not qualify as entities in the PROV framework.  SDTH focuses on the contents of data objects, not their containers.  
+
+We call the set of values assigned to a variable or dataframe at a moment time an “instance” of a data object.  Every time a command in a program changes the contents of a data object, a new instance is created.  Many instances of data objects created during the execution of a program are ephemeral and disappear when the program ends.   Only instances of data objects preserved on non-volatile media, which SDTH calls “files”, persist after the program has executed.
+
+The connection between references to data objects in the program and instances of these objects in SDTH is maintained by making variable and dataframe names properties of entities in SDTH.  Queries of SDTH can report variable/dataframe names, instances, or both.