@Override
    public String getSchema(SystemStream systemStream) {
      String fileName = String.format("%s.avsc", systemStream.getStream());
      File file = new File(schemaDir, fileName);
      try {
        return Schema.parse(file).toString();
      } catch (IOException e) {
        throw new SamzaException(e);
      }
    }
Relational schemas provider which reads system schema from a given directory
samza-sql-shell/src/main/java/org/apache/samza/sql/client/impl/FileSystemAvroRelSchemaProviderFactory.java