Tags: tutorial, advanced-user, schema, jsonschema

Conversion between LinkAhead Schema, JSON Schema, and XLSX (and vice versa)

Note

This page has been migrated from the old documentation, and has not yet been fully revised. There might be inconsistencies or errors when using with current LinkAhead versions.

This file describes the conversion between JSON schema files and XLSX templates, and between JSON data files following a given schema and XLSX files with data. This conversion is handled by the Python modules in the table_json_conversion library.

LinkAhead Schema in JSON Schema and JSON data

Let’s start with a simple Schema! If you describe a Person Record with the Properties family_name “Steve” and given_name “Stevie” in JSON, it looks like this:

{
    "Person":
        {
            "family_name": "Steve",
            "given_name": "Stevie"
        }
}

The Schema in LinkAhead defines the types of Records present in a LinkAhead instance and their structure. A LinkAhead Schema can also be represented as a JSON Schema.

You can define this kind of structure with the following JSON schema:

{
  "type": "object",
  "properties": {
    "Person": {
      "type": "object",
      "properties": {
        "family_name": {
          "type": "string"
        },
        "given_name": {
          "type": "string"
        }
      }
    }
  },
  "$schema": "https://json-schema.org/draft/2020-12/schema"
}

In general, the above schema, and any schema created by json_schema_exporter.merge_schemas(...)), describe RecordType relations and properties in dictionary form. This form is sufficient to describe a Schema, however, real data often consists of multiple entries of the same type, for example multiple Persons, which cannot be done using the schema shown above.

For example, the following JSON describes two “Person” Records:

{
    "Person": [
        {
            "family_name": "Steve",
            "given_name": "Stevie"
        },
        {
            "family_name": "Star",
            "given_name": "Stella"
        }
    ]
}

The JSON Schema for a JSON like the above one could look like the following:

{
  "type": "object",
  "properties": {
    "Person": {
      "type": "array",
      "items": {
        "type": "object",
        "properties": {
          "family_name": {
            "type": "string"
          },
          "given_name": {
            "type": "string"
          }
        }
      }
    }
  },
  "$schema": "https://json-schema.org/draft/2020-12/schema"
}

This would define that the top level object/dict may have a key Person which has as value an array of objects that in turn have the properties family_name and given_name.

You can create a data array schema from a Schema using xlsx_utils.array_schema_from_model_schema.

From JSON to XLSX: Data Representation

The following describes how JSON files representing LinkAhead records are converted into XLSX files, or how JSON files with records are created from XLSX files.

The attribute name (e.g., “Person” above) determines the RecordType, and the value of this attribute can either be an object or a list. If it is an object (as in the example above), a single record is represented. In the case of a list, multiple records sharing the same RecordType as the parent are represented.

The Properties of the record (e.g., family_name and given_name above) become columns in the XLSX file. Thus, the XLSX file created from the above example would have a sheet “Person” with the following table:

given_name	family_name
Stevie	Steve
Stella	Star

The properties of objects (Records) in the JSON have an attribute name and a value. The value can be:

1. A primitive (text, number, boolean, …)

2. A record

3. A list of primitive types

4. A list of unique enums (multiple choice)

5. A list of records

In cases a. and c., a cell is created in the column corresponding to the property in the XLSX file. In case b., columns are created for the Properties of the record, where for each of the Properties the cases a. - e. are considered recursively. Case d. leads to a number of columns, one for each of the possible choices.

For case e. however, the two-dimensional structure of an XLSX sheet is not sufficient. Therefore, for such cases, new XLSX sheets/tables are created.

In these sheets/tables, the referenced records are treated as described above (new columns for the Properties). However, there are now additional columns that indicate from which “external” record these records are referenced.

Let’s now consider these five cases in detail and with examples:

a. Properties with primitive data types

{
    "Training": [
      {
        "date": "2023-01-01",
        "url": "www.indiscale.com",
        "duration": 1.0,
        "participants": 1,
        "remote": false
      },
      {
        "date": "2023-06-15",
        "url": "www.indiscale.com/next",
        "duration": 2.5,
        "participants": null,
        "remote": true
      }
    ]
}

This entry will be represented in an XLSX sheet with the following content:

date	url	duration	participants	remote
2023-01-01	www.indiscale.com	1.0	1	false
2023-06-15	www.indiscale.com/next	2.5		true

b. Property referencing a record

{
    "Training": [
      {
        "date": "2023-01-01",
        "supervisor": {
            "family_name": "Stevenson",
            "given_name": "Stevie"
        }
      }
    ]
}

This entry will be represented in an XLSX sheet named “Training” with the following content:

date	supervisor.family_name	supervisor.given_name
2023-01-01	Stevenson	Stevie

c. Properties containing lists of primitive data types

{
    "Training": [
      {
        "url": "www.indiscale.com",
        "subjects": ["Math", "Physics"],
      }
    ]
}

This entry would be represented in an XLSX sheet with the following content:

url	subjects
www.indiscale.com	Math;Physics

The list elements are written into the cell separated by a semicolon (;). If the elements contain the separator ;, it is escaped with \.

d. Multiple choice properties

{
    "Training": [
      {
        "date": "2024-04-17",
        "skills": [
              "Planning",
              "Evaluation"
        ]
      }
    ]
}

If the skills list is denoted as an enum array with "uniqueItems": true in the json schema, this entry would be represented like this in an XLSX:

date	skills.Planning	skills.Communication	skills.Evaluation
2024-04-17	x		x

Note that this example assumes that the list of possible choices, as given in the json schema, was “Planning, Communication, Evaluation”.

e. Properties containing lists with references

{
    "Training": [
      {
        "date": "2023-01-01",
        "coach": [
            {
              "family_name": "Sky",
              "given_name": "Max",
            },
            {
              "family_name": "Sky",
              "given_name": "Min",
            }
        ]
      }
    ]
}

Since the two coaches cannot be represented properly in a single cell, another worksheet is needed to contain the properties of the coaches.

The sheet for the Trainings in this example only contains the “date” column

date
2023-01-01

Additionally, there is another sheet where the coaches are stored. Here, it is crucial to define how the correct element is chosen from potentially multiple “Trainings”. In this case, it means that the “date” must be unique.

The second sheet looks like this:

date	coach.family_name	coach.given_name
2023-01-01	Sky	Max
2023-01-01	Sky	Min

Note: This uniqueness requirement is not strictly checked right now, it is your responsibility as a user that such “foreign properties” are truly unique.

When converting JSON files which contain Records that were exported from LinkAhead, it can be a good idea to use the LinkAhead ID as a unique identifier for Records. However, if your Records do not yet have LinkAhead IDs, you need to define another identifying properties/foreign keys. Note that these properties only need to identify a Record uniquely within the list of Records: In the above example the “coach” Record needs to be identified in the list of coaches.

Data in XLSX: Hidden automation logic

First column: Marker for row types

The first column in each sheet is used to annotate special rows with metadata, and is hidden by default. The following values are used:

• IGNORE: This row is ignored. It can be used for explanatory texts or layout.

• COL_TYPE: Typically the first row that is not IGNORE. It indicates the row that defines the type of columns (FOREIGN, SCALAR, LIST, MULTIPLE_CHOICE, IGNORE). This row must occur exactly once per sheet.

• PATH: Indicates that the row is used to define the path within the JSON. These rows are typically hidden for users.

An example table could look like this:

IGNORE		Welcome	to	this	file
IGNORE		Please	enter your	data here:
COL_TYPE	IGNORE	SCALAR	SCALAR	LIST	SCALAR
PATH		Training	Training	Training	Training
PATH		url	date	subjects	supervisor
PATH					email
IGNORE	Please enter one training per line.	Training URL	Training date	Subjects	Supervisor’s email
		example.com/mp	2024-02-27	Math;Physics	mailto:steve@example.com
		example.com/m	2024-02-28	Math	mailto:stella@example.com

Parsing XLSX data

To extract the value of a given cell, we traverse all path elements (in PATH rows) from top to bottom. The final element of the path is the name of the Property to which the value belongs. In the example above, steve@example.com is the value of the email Property in the path ["Training", "supervisor", "email"].

The path elements are sufficient to identify the object within a JSON, at least if the corresponding JSON element is a single object. If the JSON element is an array, the appropriate object within the array needs to be selected.

For this selection additional FOREIGN columns are used. The paths in these columns must all have the same base and one additional unique key component. For example, two FOREIGN columns could be ["Training", "date"] and ["Training", "url"], where ["Training"] is the base path and "date" and "url" are the unique keys.

The base path defines the table (or recordtype) to which the entries belong, and the values of the unique keys define the actual rows to which data belongs.

For example, this table defines three coaches for the two trainings from the last table:

COL_TYPE	FOREIGN	FOREIGN	SCALAR
PATH	Training	Training	Training
PATH	date	url	coach
PATH			given_name
IGNORE	Date of training	URL of training	The coach’s given name
IGNORE	from sheet ‘Training’	from sheet ‘Training’
	2024-02-27	example.com/mp	Ada
	2024-02-27	example.com/mp	Berta
	2024-02-28	example.com/m	Chris

Special case: multiple choice “checkboxes”

As a special case, enum arrays with "uniqueItems": true can be represented as multiple columns, with one column per choice. The choices are denoted as the last PATH component, the column type must be MULTIPLE_CHOICE.

Stored data is denoted as an “x” character in the respective cell, empty cells denote that the item was not selected. Additionally, the implementation also allows TRUE or 1 for selected items, and FALSE, 0 or cells with only whitespace characters for deselected items:

COL_TYPE	MULTIPLE_CHOICE	MULTIPLE_CHOICE	MULTIPLE_CHOICE
PATH	skills	skills	skills
PATH	Planning	Communication	Evaluation
IGNORE	skills.Planning	skills.Communication	skills.Evaluation
	x		X
	“ “	TRUE	FALSE
	0	x	1

These rows correspond to:

1. Planning, Evaluation

2. Communication

3. Communication, Evaluation

User Interaction

The primary and most straight forward use case of this utility is to export LinkAhead data as JSON and then as XLSX tables. This can be done fully automatic.

The hidden cells for automation are designed such that the XLSX template that is created can be customized such that it is a nicely formatted table. The hidden content must remain. See below for tips on how to manipulate the table.

The second use case is to use XLSX to collect data and then import it into LinkAhead. Here, it may be necessary to define foreign keys in order to identify Records in lists.

Table Manipulation

• All formatting is ignored

• Nothing has to be observed when adding new data rows

• When adding new descriptory rows (for example one for descriptions of the columns), the COL_TYPE must be set to IGNORE

• You can freely rename sheets.

• You can freely rename columns (since the row containing the column names is set to IGNROE; the Property name is taken from the last path element)

• You can change the order of columns. However, you have to make sure to move the full column including hidden elements. Thus, you should not select a range of cells, but click on the column index in your spreadsheet program.

Note: Requirements

This conversion does not allow arbitrary JSON schema files nor does it support arbitrary JSON files since conversion to XLSX files would not make sense. Instead, this utility is tailored to supported conversion of data (and Schema) that are structured like data (and Schema) in LinkAhead:

• The JSON Schema describes a Schema of RecordTypes and Properties as it would be generated by the caosadvancedtools.json_schema_exporter module.

• The JSON files must contain arrays of Records complying with such a Schema.

Thus, when converting from a JSON schema, the top level of the JSON schema must be a dict. The keys of the dict are RecordType names.