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== Incremental Schema ==
DataStore is designed for sharing data among applications. Applications will assume data types of attributes of objects in a data store. If the data type of an attributes is not consistent among applications, applications will be broken for read data from other applications with different assumption on the data type. That is why the data types of attributes should be enforced.
Every object in a data store is a tree. The path from root to any node can be represented as an ordered list of attribute names. Incremental schema is to define the type of an attribute while the path of the attribute was found first time. In an other word, once a new object was added to a data store, its tree of attributes will be traveled, and assigned the type of new attributes as the type of their values. A new attribute is one attribute whose path from root is never found before in a data store.
For example, if the following object is the object been added to a data store.
{
SN: 123,
name: "John Lin",
info: {
address: ".....",
birth: Date(....),
}
}
Then, the table of types of attributes should be
SN: Integer
name: String
info: object
info address: String
info birth: Date
Then, the following object is added.
{
SN: 123,
name: "John Lin",
info: {
address: ".....",
birth: Date(....),
phone: "123456",
}
}
The table of types of attributes should be
SN: Integer
name: String
info: object
info address: String
info birth: Date
info phone: String
Every time a new object was added to a data store, the types of attributes of the object would be checked against the types table of the data store. The action of adding will be failed if the type of any attribute does not match the type defined in the types table.
== Issues ==
* What's happening if the central gets changes during the process of local updates?
* |addedIds|, |removedIds| and |updatedIds| arrays should be synchronized. For example, the ID of record that has been updated and removed should only show up in the |removedIds| array. Need to define the behaviours.
* Should all data stores with the name share a schema?
