"HELIO Data Collections are used to store a lists of structured data withing your HMI, not on your PLC. This kind of data is often too large to be handled as a whole on your PLC, which is often only interested in specific properties of a collection item.

• HELIO uses simple JSON files to store those collections on the device that executes the HELIO Runtime.
• Each file and therefore item hast to follow the same schema, be it for recipes, tools, or tasks.
• In some cases, other software components may even read, write, and delete files in the same collection. Meanwhile, HELIO monitors changes and notifies all connected HMIs.”

The Different Kind of Data Collections

MANAGED COLLECTIONS

For Managed Collections, HELIO will handle most tasks, including selecting the storage location and creating unique keys that identify each item.

Although Managed Collections have limitations, they also relieve you of most decision-making responsibilities.

UN-MANAGED COLLECTIONS

Unmanaged Collections provide more control over both the storage location and the unique key attribute of a collection.

Unmanaged Collections are often used as very a simple API interface between your HMI and external backend services (e.g. PLC or other software services that run on your target device).

When to use?

MANAGED

• You require a storage solution for a set of structured data.
• Your backend service requires certain data from the collection, but the HMI provides it through the PLC Connection (Data Source Type) , such as an OPC UA Connection (PLC Connection Type).
• The HMI uses the following actions to provide data to your backend:
  • Call Data Method (Action)
  • Write Data Variable (Action)

UN-MANAGED

• You require a storage solution for a set of structured data.
• Your backend needs direct file access to the large structured data because…
  • …it stores additional metadata, files, or assets for each item.
  • …it needs the ability to create, store or update items in this collection.
• You have a third-party application or service that requires access to this data, such as an MES System or Reporting System.

How Does HELIO Store Collection Data?

MANAGED

• The collection is stored in a directory within the HELIO Data Directory , the so called Collection Directory. The name and the location of this directory are hidden from you.
• Each item inside the Collection Directory is stored as a separate folder, the so called Item Directory.
• HELIO creates unique IDs for each item to make sure they are one of a kind. But, these internal IDs won't be shown to the users of the collection. The Item Directory is named after the unique key that identifies the item.
• All the properties of an item are stored in a file called data.json inside the Item Directory.

UN-MANAGED

• The collection is stored in the directory you specify during the creation of the collection. It can be within or outside of the HELIO Data Directory.
• Each item inside the Collection Directory is stored as a separate folder, the so called Item Directory.
• The creator of an item must ensure its uniqueness. This is determined by the Key attribute, which is specified during the creation of the collection.
• Each Item Directory will be named by its Key attribute.
• All the properties of an item are stored in a file called data.json inside the Item Directory.

How Does It Look in the File System?

MANAGED

The folder aD73L5TqQqyOd56Uns-swg is an example of a Managed Collection. It’s name and also the names of its Item Directories have all autogenerated by HELIO.

UN-MANAGED

The folder DataCollectionExampleUnmanaged is an example of an Unmanaged Collection. It’s name has been chosen by the HMI Engineer, and the name of its Item Directories are generated by the HMI.

How Does It Look in the HMI Data Tree of My Project?

MANAGED

The DataCollectionExampleManaged does not include its internal unique key.

UN-MANAGED

The DataCollectionExampleUnmanaged list includes the CustomID property, which can be both read and written by the HMI.

How Is Uniqueness Guaranteed?