update in ms excel compatible formats documentation (#20)

Author: Maks-D

src/SUMMARY.md

@@ -14,7 +14,7 @@
         - [NDJSON](config/dataset-formats/ndjson.md)
         - [Delta Lake](config/dataset-formats/delta.md)
         - [Arrow](config/dataset-formats/arrow.md)
-        - [Xlsx](config/dataset-formats/xlsx.md)
+        - [MS Excel compatible formats](config/dataset-formats/excel.md)
     - [Blob store](./config/blob-store.md)
     - [Databases](./config/databases.md)
 - [Postgres wire protocol](postgres.md)

src/config/dataset-formats/excel.md

@@ -0,0 +1,88 @@
+# MS Excel compatible formats.
+
+ROAPI supports loading a few Microsoft Excel compatible formats like xls, xlsx, xlsb, ods.
+
+## Configuration
+To load MS Excel compatible files the config should be specified like:
+```yaml
+tables:
+    - name: "<table name>"
+      uri: "<files path>"
+      option:
+        format: "<file format>"
+        sheet_name: "Sheet1"
+        rows_range_start: 2
+        rows_range_end: 5
+        columns_range_start: 1
+        columns_range_end: 6
+        schema_inference_lines: 3
+```
+* **format** - name of file format. Currently supported files format:
+    * xls (Microsoft Excel 5.0/95 Workbook)
+    * xlsx (Excel Workbook)
+    * xlsb (Excel Binary Workbook)
+    * ods (OpenDocument Spreadsheet)
+* **sheet_name** - the name of the spread sheet with table data. By default, most files initially use Sheet1 as the `sheet_name`. Be sure to change this `sheet_name` as needed if your spreadsheet uses a different name.
+![xlsx_sheet_name](../../images/xlsx_sheet_name.png)
+If no `sheet_name` is specified, ROAPI will use first spreadsheet.
+* **Table range options**
+    * **rows_range_start** - the first row of the table. It contains column names. By default, `rows_range_start` is 0 (the first raw in spreadsheet)
+    * **rows_range_end** - the last row of the table. By default, ROAPI reads all data.
+    * **columns_range_start** - the column of the table. By default, `columns_range_start` is 0 (first column in spreadsheet)
+    * **columns_range_end** - the last column of the table. By default, ROAPI reads all columns.  
+For example, to take only selected data:
+  ![spread_sheet_range](../../images/spread_sheet_range.png)
+  the config file looks like:
+```yaml
+tables:
+    - name: "<table name>"
+      uri: "<files path>"
+      option:
+        format: "<file format>"
+        sheet_name: "Sheet1"
+        rows_range_start: 1
+        rows_range_end: 4
+        columns_range_start: 1
+        columns_range_end: 3
+```
+* **schema_inference_lines** - the number of rows (inside table range) to use in schema inference. This number includes the row with column names, so, for example, `schema_inference_lines: 3` means ROAPI will use first row for column names inference and 2 rows for column types inference. If this option is not specified then ROAPI reads all rows for column data types inference.
+
+## Schema inference. 
+ROAPI can infer schema of data automatically. The first row of data range is a row with column names. After column names inference ROAPI will infer data types by scanning all remaining rows or limited number of rows specified in `schema_inference_lines` option.
+If column contains more than one data type (for exaple, float and int) then ROAPI use Utf8 datatype.
+
+Also, it is possible to specify schema in configuration file. This allows to avoid schema inference from data and loading of table will be faster.
+
+```yaml
+tables:
+    - name: "excel_table"
+      uri: "path/to/file.xlsx"
+      option:
+        format: "xlsx"
+      schema:
+        columns:
+        - name: "int_column"
+          data_type: "Int64"
+          nullable: true
+        - name: "string_column"
+          data_type: "Utf8"
+          nullable: true
+        - name: "float_column"
+          data_type: "Float64"
+          nullable: true
+        - name: "datetime_column"
+          data_type: !Timestamp [Seconds, null]
+          nullable: true
+        - name: "duration_column"
+          data_type: !Duration Second
+          nullable: true
+        - name: "date32_column"
+          data_type: Date32
+          nullable: true
+        - name: "date64_column"
+          data_type: Date64
+          nullable: true
+        - name: "null_column"
+          data_type: Null
+          nullable: true
+```