# FAQ and Troubleshooting

## What can and can not be changed/deleted **BEFORE** publishing?

You can change and delete everything except the schema can not be deleted.

## What can and can not be changed/deleted AFTER publishing?

You **can change** the name of the schema or of the attribute. You can also change the unit of an attribute.\
You **can not change** the key of a schema or attribute. You can not also change the data type or the decimals of an attribute.

## Which data type should I use for which attribute?

* **String** for text or single characters (variable unlimited length).
* **Boolean** for true/false values.
* **Long, Integer** (64 bit/32 bit) for signed and unsigned integers.
* **Double** (64 bit) floating-point number for representation of decimals.
* **Timestamp** for UNIX timestamps in milliseconds.
* **Time** is not used anymore (deprecated).
* **None** is not used anymore (deprecated).

All columns are also allowed to have NULL entries.

## Do I need to define attributes like Thing or Timestamp as well?

No, the Thing and Timestamp columns are metadata. Every schema automatically has all metadata columns, which are: Id, Inserted, Size, Thing, Timestamp, Type.

## The messages sent include all attributes defined in the event schema but the messages are put into "invalid messages". Why?

This could have several different reasons.

1. Any value in the message is of the wrong data type
2. Any value in the message includes an unexpected symbol
3. There are some additional attributes that are not defined in the event schema


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