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---
title: Welcome to gCube Catalogue Service (aka gCat) documentation
---
gCat is a RESTful application which exposes operations via REST-API.
See the available [REST-API docs](../api-docs/index.html).
Base URL
========
In the production environment, its current value is
<https://api.d4science.org/gcat>
Authorization
=============
D4Science adopts state-of-the-art industry standards for authentication
and authorization. Specifically, the implementation fully adopts [OIDC
(OpenID Connect)](https://openid.net/connect) for authentication and UMA
2 (User-Managed Authorization) for authorization flows. [JSON Web Token
(JWT) Access token](https://jwt.io/) are used for both authentication
and authorization.
Obtain your Bearer token here:
<https://dev.d4science.org/how-to-access-resources>
Service
=======
You can call the methods of the Web Service by writing your own REST
client application or using existing REST client plugins.
HTTP Statuses
-------------
Any successful operation returns *200 OK* HTTP status code. The create
operation returns *201 Created*. Any Background operation returns *202
Accepted*. Any operation which does not provide any content return *204
No Content*.
The most common error status a client can obtain are:
- **400 Bad Request** used to indicate a clients error
<https://tools.ietf.org/html/rfc7231#section-6.5.1>;
- **401 Unauthorized** used to indicate that the client does not
provide the authorization token in the HTTP Header or the client has
not enough right to perform such request
<https://tools.ietf.org/html/rfc7235#section-3.1>;
- **404 Not Found** used to indicate that the requested instance does
not exist <https://tools.ietf.org/html/rfc7231#section-6.5.4>;
- **405 Method Not Allowed** the used HTTP method is not supported for
the requested URL
<https://tools.ietf.org/html/rfc7231#section-6.5.5>. The response
contains the *Allow* HTTP Header indicating the supported HTTP
method for such URL
<https://tools.ietf.org/html/rfc7231#section-7.4.1>;
- **409 Conflict** the request could not be completed due to a
conflict with the current state of the target resource (e.g. the
name of the resource already exists)
<https://tools.ietf.org/html/rfc7231#section-6.5.8>;
- **500 Internal Server Error** indicate a server failure
<https://tools.ietf.org/html/rfc7231#section-6.6.1>.
You can find a complete list of HTTP Status at
<https://httpstatuses.com/>
If you get a *500 Internal Server Error*, please report it in the [gCube
ticketing system](https://support.d4science.org).
Please use this checklist before reporting an error:
- Replicate the request;
- The failure could be temporal due to network error, server issue and
many other temporal issues. For this reason, please retry the
request after a certain amount of time before reporting the issue;
- indicate how to replicate the error;
- indicate the time when the error occurred (this simplifies
identifying the issue).
HTTP Methods
------------
gCat is a pure RESTful service. It uses standard HTTP Methods to perform
listing of collections and CRUD (Create Read Update Delete) operations
on instances.
:::{table} Supported operations
:align: center
:widths: grid
| Operation | HTTP Method | URL | Success HTTP Status | Safe | Idempotent |
| ------------------------------ | ----------- | -------------------------------------- | ------------------- | ---- | ---------- |
| **Supported<br/>HTTP Methods** | OPTIONS | /{COLLECTION} | 204 No Content | Y | Y |
| **List** | GET | /{COLLECTION} | 200 OK | Y | Y |
| **Count** | GET | /{COLLECTION}?count=true | 200 OK | Y | Y |
| **Exists** | HEAD | /{COLLECTION} | 204 No Content | Y | Y |
| **Create** | POST | /{COLLECTION} | 201 Created | N | N |
| **Supported<br/>HTTP Methods** | OPTIONS | /{COLLECTION}/{INSTANCE_ID} | 204 No Content | Y | Y |
| **Exist** | HEAD | /{COLLECTION}/{INSTANCE_ID} | 204 No Content | Y | Y |
| **Read** | GET | /{COLLECTION}/{INSTANCE_ID} | 200 OK | Y | Y |
| **Update** | PUT | /{COLLECTION}/{INSTANCE_ID} | 200 OK | N | Y |
| **Patch** | PATCH | /{COLLECTION}/{INSTANCE_ID} | 200 OK | N | Y |
| **Delete** | DELETE | /{COLLECTION}/{INSTANCE_ID} | 204 No Content | N | N |
| **Purge** | PURGE | /{COLLECTION}/{INSTANCE_ID} | 204 No Content | N | N |
| **Purge** | DELETE | /{COLLECTION}/{INSTANCE_ID}?purge=true | 204 No Content | N | N |
### About URL
The presented URL uses the following convention:
- **{COLLECTION}** is the plural name of the entity type;
- **{INSTANCE\_ID}** is an identification that enables univocally
identifying the instance in the collection.
### About Safety and Idempotency properties
- A method is *Safe* if it does not produce any side effects. \"This
does not prevent an implementation from including behaviour that is
potentially harmful, that is not entirely read-only, or that causes
side effects while invoking a safe method\"
<https://tools.ietf.org/html/rfc7231#section-4.2.1>;
- A method is *Idempotent* if the same operation repeated multiple
times has the same side effect than using it one time. \"repeating
the request will have the same intended effect, even if the original
request succeeded, though the response might differ\"
<https://tools.ietf.org/html/rfc7231#section-4.2.2>.
You can find more information about HTTP Methods at
<https://restfulapi.net/http-methods/>
### Uncommon HTTP Methods
- PATCH method allows to perform a differential update (i.e. an update
which provides only the differences and not the whole new
representation);
- PURGE method is not a standard but is widely used in service which
requires this action (e.g.
[Varnish](https://varnish-cache.org/docs/3.0/tutorial/purging.html),
[Squid](https://wiki.squid-cache.org/SquidFaq/OperatingSquid#How_can_I_purge_an_object_from_my_cache.3F)).
gCat provides support for this method, but to support a wider range
of clients, it also provides the Purge action via *DELETE* with the
additional get parameter `purge=true`.
Content-Type
------------
Any request must contain an indication of the interesting content type.
The client must specify the **Accept** HTTP Header for any operation
returning a result.
``` {.rest}
Accept: application/json
```
For any operation sending content to the service, it is necessary to
specify the **Content-Type** HTTP Header.
``` {.rest}
Content-Type: application/json
```
The service accepts and returns only JSON objects.
[Profile Collection](../api-docs/resource\_Profile.html) instead can be
manipulated in XML only.
Collections
-----------
The following collections are available to any user. Catalogue-Editor or
above can invoke Non-safe methods only.
- [Item Collection](../api-docs/resource_Item.html);
- [Resource Collection](../api-docs/resource_Resource.html);
- [Profile Collection](../api-docs/resource_Profile.html);
- [Namespace Collection](../api-docs/resource_Namespace.html);
- [License Collection](../api-docs/resource_License.html);
- [Trash Collection](../api-docs/resource_Trash.html);
The following collections are available for Catalogue-Admins or above
only:
- [Group Collection](../api-docs/resource_Group.html);
- [Organization Collection](../api-docs/resource_Organization.html);
- [User Collection](../api-docs/resource_User.html);
- [Configuration Collection](../api-docs/resource_Configuration.html).
An overview of the available collections is available at
[../api-docs/index.html](../api-docs/index.html);
Roles
-----
Any user has one or more roles in the catalogue. Only the VRE Manager
can assign roles to VRE users.
The catalogue uses the following hierarchic roles:
**Catalogue-Member**:
: A user with such a role is mainly capable of listing and reading
items;
**Catalogue-Editor**:
: A user with such a role is capable of managing the items he/she
creates and capable of using other safe APIs;
**Catalogue-Admin**:
: A user with such a role is capable of administrating many aspects of
the catalogue;
**Catalogue-Manager**:
: A user with such a role can use all the APIs exposed by the service
except item moderation APIs (e.g. approve, reject, \...).
Another role that is not in the role hierarchy:
**Catalogue-Moderator**:
: A user with such a role is capable of invoking the item moderation
APIs.
::: {.tip}
::: {.title}
Tip
:::
:::
Please note that not all catalogues are moderated.
Moderated Catalogues
====================
Any catalogues can be declared as moderated. This means that, a
**Catalogue-Moderator** must approve any submitted items to make them
available to the other users of the catalogue.
In a moderated catalogue, an item can be in the following states:
**pending**:
: The item published by any allowed author (a Catalogue-Editor or
above) but not available to the other users of the catalogue. A
Catalogue-Moderator has to approve or reject it;
**approved**:
: A Catalogue-Moderator has approved the item published by any allowed
users;
**rejected**:
: A Catalogue-Moderator has rejected the item published by any allowed
users.
The following are the moderation operations that an allowed user can
perform on an item. To present the moderation operations, we use the
following convention:
> `initial_state` \-\--**operation** (*User/Role performing the
> operation*)\-\--\> `final_state`
`initial_state` can be `none`, meaning the item does not exist.
The following are the allowed moderation operation on an item
> `none` \-\--**create** (*Author*)\-\--\> `pending`
>
> `pending` \-\--**reject** (*Catalogue-Moderator*)\-\--\> `rejected`
>
> `pending` \-\--**approve** (*Catalogue-Moderator*)\-\--\> `approved`
>
> `rejected` \-\--**update** (*Author*)\-\--\> `pending`
>
> `approved` \-\--**update** (*Author*)\-\--\> `pending`
Please check the table below whcih summarise the item collection
operation and the allowed users/roles.
In a moderated catalogue, both the Catalogue-Moderators and the item
author can send messages to discuss the approval process of the item.
The messages are related to a specific item. Any Catalogue-Moderators
receive a message sent by an Author. The author receives a message sent
by a Catalogue-Moderator as well as the other Catalogue-Moderators (if
any).
Messages can be sent both with an action which changes the status of the
item or as explicit action which does not change the status of the item:
> `pending` \-\--**message** (*Author OR Catalogue-Moderator*)\-\--\>
> `pending`
>
> `rejected` \-\--**message** (*Author OR Catalogue-Moderator*)\-\--\>
> `rejected`
>
> `approved` \-\--**message** (*Author OR Catalogue-Moderator*)\-\--\>
> `approved`
The following table summarize the allowed/forbidden operations depending
on: the role of the user and the state of the item.
The Moderation process has associated notification to authors and
Catalogue-Moderators. Please note that the user who has acted is not
self-notified, e.g. approve operation made by a Catalogue-Moderator
notifies the item author and the other Catalogue-Moderators of the VRE.
The following table summarises the addressee of the notification for any
action.
Java Client
===========
We provide the following Java Client out-of-the-box.
> ::: {.tip}
> ::: {.title}
> Tip
> :::
>
> If you\'re coding in Java, it is recommended that you use this Java
> Client.
> :::
**Maven Coordinates**
``` {.xml}
<groupId>org.gcube.data-catalogue</groupId>
<artifactId>gcat-client</artifactId>
<version>[2.2.0, 3.0.0-SNAPSHOT)</version>
```
**Methods Result**
The service exposes [its methods](../api-docs/index.html) using a
standard naming approach. Moreover, they accept (in the case of HTTP
POST/PUT methods) JSON objects.
> ::: {.important}
> ::: {.title}
> Important
> :::
>
> The result of all methods is always a JSON object as per below:
> :::
``` {.javascript}
{
"rating": 0.0,
"license_title": "Creative Commons Attribution Share-Alike 4.0",
"maintainer": "Frosini Luca",
"relationships_as_object": [],
"private": false,
"maintainer_email": "luca.frosini@isti.cnr.it",
"num_tags": 1,
"id": "17051d86-c127-4928-9296-d3d7590161fe",
"metadata_created": "2022-10-17T12:45:53.118318",
"metadata_modified": "2022-10-18T10:30:03.362756",
"author": "Frosini Luca",
"author_email": "luca.frosini@isti.cnr.it",
"state": "active",
"version": null,
"creator_user_id": "f1b0265c-9983-4f97-a7b6-be3cc0544b27",
"type": "dataset",
"resources": [],
"num_resources": 0,
"tags": [
{
"vocabulary_id": null,
"state": "active",
"display_name": "Test",
"id": "fec9de86-51a2-41b0-aef4-ba06eb39e16d",
"name": "Test"
}
],
"groups": [],
"license_id": "CC-BY-SA-4.0",
"relationships_as_subject": [],
"organization": {
"description": "",
"created": "2016-05-30T11:30:41.710079",
"title": "devVRE",
"name": "devvre",
"is_organization": true,
"state": "active",
"image_url": "",
"revision_id": "a7eee485-a6d5-4a7b-8f73-b0ed999d5b03",
"type": "organization",
"id": "3571cca5-b0ae-4dc6-b791-434a8e062ce5",
"approval_status": "approved"
},
"name": "my_test_item_devvre",
"isopen": true,
"url": "http://www.d4science.org",
"notes": "A test item of Luca Frosini",
"extras": [
{
"key": "Item URL",
"value": "https://data.dev.d4science.org/ctlg/devVRE/my_test_item_devvre"
},
{
"key": "Language",
"value": "EN"
},
{
"key": "system:cm_item_status",
"value": "approved"
},
{
"key": "system:cm_item_visibility",
"value": "public"
},
{
"key": "system:type",
"value": "EmptyProfile"
}
],
"license_url": "https://creativecommons.org/licenses/by-sa/4.0/",
"ratings_count": 0,
"title": "My Test Item",
"revision_id": "bc0d1f2a-4e97-4810-b951-8b72e8279719"
}
```
*Inputs are automatically validated before the request is served.*
**Usage examples**
- Example 1
``` {.java}
import org.gcube.gcat.client.Item;
// count item number
Item item = new Item();
int count = item.count();
...
```
Service Discovery on IS
=======================
The service can be discovered in the gCore IS as gCore Endpoint with the
following parameter:
``` {.xml}
<ServiceClass>org.gcube.data-catalogue</ServiceClass>
<ServiceName>gcat</ServiceName>
```
The service can be discovered in the Facet Based IS as EService with the
following json query:
``` {.json}
{
"@class": "EService",
"consistsOf": [
{
"@class": "IsIdentifiedBy",
"target": {
"@class": "SoftwareFacet",
"group": "org.gcube.data-catalogue",
"name": "gcat"
}
}
]
}
```
Service Maven Coordinates
=========================
The maven coordinates of gCat service are:
``` {.xml}
<groupId>org.gcube.data-catalogue</groupId>
<artifactId>gcat</artifactId>
```
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