Thursday, August 21, 2008

Guidelines for defining data models

TR-106 defines data model guidelines for creating new data models. For interoperability and to provide better clarity, I have defined some more guidelines.

Before you proceed further, please read this.


Guidelines that are being followed today in defining data models.

  • Data type: such as string, base64, integer, unsigned integer, Boolean, char etc..
  • Range: In case of integer, unsigned integer values.
  • Enumerations: Set of values that this parameter can take. Valid for both integers and strings.
  • Min/Max length of string: In case of string and base64 types.
  • Read/RW attributes for parameters
  • Create/Delete for table nodes.

Additional guidelines:


  1. Values of some parameters don't reflect changes done by ACS. These are called action parameters. Each action parameter should have associated result parameter. Action parameters are always strings and it takes value "apply". ACS sets this value to perform the action. These parameters should be defined with attribute called "ActionParameter". This attribute should be set to 1 for action parameters. Associated result parameter fully qualified name should also be set with attribute "AssociatedResultParameterName".
  2. For each associated action parameter, there should be result parameter. Result parameters are always strings. "success", "not available" are two values defined by this guidelines. Any other string value is considered as error in performing the action by application. Possible error strings are defined by applications defining the data model. Whenever action parameter value is set, associated result string value should get automatically set to "not available". When the application processing is done successfully, then this parameter value would be set to "success" by device. If application processing returns error, appropriate string value is set to this parameter.
  3. Always define default values for all parameters except for mandatory parameters of table objects.

Table objects:

  1. Identify the parameter that uniquely identifies the instance in the table object. Indicate that in an attribute "KeyParameter". ACS can check for the uniqueness of this value whenever the instance is created.
  2. For each parameter that can't be changed after instance is created, indicate in DM that "DontChangeAfterCreate". Key parameter of the table object typically has this attribute set. There could be other parameters too based on application.
  3. Identify all parameters that are mandatory during instance creation. Use "Mandatory" attribute for these parameters. ACS can ensure to send values for all mandatory parameters in "SetParameterValues" method that follows "AddObject" RPC method.
  4. Indicate the default value in the data model if the parameter is not mandatory. This information is needed when ACS user asks it to reset the some specific optional parameter to default value.
  5. For every table object, one parameter "Number Of Entries" must be present as per TR-106. I suggest to have one parameter "Number off Entries Supported" to represent the number of rows the device can hold. Both these parameters take integer values and both of them are READONLY. Note that names of the parameters could be different for different data models (table nodes). Hence there is need to associate these parameters to appropriate table nodes. To associate these parameters for the table object (table node), these parameter should have attributes associated with it indicating the full qualified table object. I call this attribute as "AssociatedTableNode". In addition to this attribute, two more attributes are needed - "CurrentEntriesIndicator", "MaxNumEntriesIndicator". CurrentEntriesIndicator attribute should be set to parameters indicating the current number of entries and MaxNumEntriesIndicator attribute should be set to parameters indicating the maximum number of entries that device can take for corresponding table.
  6. If table is representing the ordered list, then it should have special attribute for the table object called "OrderList". Also it should have associated parameter name that indicate the priority of the ordered list. Call this attribute as "PriorityParameterName". This information is used by ACS as described in previous blog here. Priority parameter name takes integer values. Lower values indicate higher priority instances.
  7. If table is an ordered list, it should also have one pair of action and result parameters for revalidation purposes. In addition to attributes it defined earlier for these two parameters, it should have additional parameter representing the table object name with attribute "AssociatedTableNode". ACS uses these attributes to know the parameters names to revalidate the states in the device.
  8. As described under section "Nested table objects and special cases" of earlier blog here, there is a need for creating a table object instance with at least one instance of child table. ACS needs to know this special relationship so that it generates the screens such a way that it takes at least one child instance parameters as part of parent instance creation screen. This relationship information also useful for ACS to validate this information before sending configuration to devices. Each child table of this type should have one attribute "OneInstanceNeededByParent" set to 1.

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