ISO PAS 22720:2005 pdf download ASAM Open Data Services 5.0
1.2.1 THE DATA MODEL
The first and most important aspect of ASAM ODS is its data model.Typically there are different levels to exchange a data item.Two systems or software packages might not be able to exchange this data item at all.This is the case if e.g. system A expects the data item to be represented as a 4-bytefloating point number while system B expects it to be represented by a 2-byte integervalue.
The drawback is obvious: no automatic data exchange can be set up without changingeither of the systems (that is: its software).
Two systems or software packages may be able to exchange this data item as a numberbecause the data representation of the item is the same on both systems. This capabilityoften is the result of some standardization effort, specifying universal data formats. Anexample is the wide-spread CSV (comma separated values) format, where data itemsare represented by an ASCll string, and consecutive data items are separated from eachother by a comma. System A may produce such a CSV file and system B may be able toread it and know about the numbers contained in it.The drawback is still obvious: without additional knowledge about the meaning of thedata item its value is quite useless.
Similarly two systems or software packages may be able to exchange this data item as anumber with a name e.q. because a common database is used. ln this case system Astores the value of the data item in some place in a table, using a row and/or columnname; this is typically done through some database interfaces, System B may now usethe same database interfaces, identify the data item by its name and/or location in thetable and thus get back its value.The drawback is not very obvious; it seems that the data item is fully described by (i) itsvalue and (li) its name. However, its value is only useful if the retrieving system B knowsabout the meaning of the data item’s name. This requires additional conventions onnaming of data items. And questions like “What unit belongs to the value?”,“ls this themost recent of a set of available values for the data item?” etc. still remain open.
Some data exchange solutions overcome this drawback by specifying everything.Examples can be found looking at some serial interface protocol specifications or atsome quite fixed database models. Though this provides a maximum of informationprovision, such solutions proved to be very inflexible and are tailored to the needs of onespecific task.ASAM ODS headed for an optimum compromise.
On the one hand the specifications shall be applicable to a variety of application areas. Datagathered from small vehicle parts shall be accessible in the same way as those of completevehicles. Data taken in overseas shall be available together with on-site data (regardless ofthe language, unit schemes, etc.). Data from research projects as well as from productionprocesses or even after-sales information shall be exchangeable, All systems involved in anyof those steps shall be able to store and retrieve data based on the ASAM ODS data model.And, since large amounts of data already are existing all over the companies, ASAM ODSshould provide some means to integrate them into the new approach.
On the other hand the information stored shall still be valuable and contain enough meaningto allow some automatic retrieval and data analysis. There should be a relation between adata value (the number) and a corresponding unit in order to know about the real physicalvalue, There should be a relation between the data item and the vehicle or part where it wastaken, and with what equipment it has been taken, and who has taken it, and so on.
This finally led to the current data model of ASAM ODS. It distinguishes between a so calledbase model’and an ‘application model.
The base model is a set of defined base elements and a set of base relations between them.Each base element represents a type of information, E.g. ‘AoUnit is the base element thatrepresents information on a physical unit (like Newton, Kelvin.,..), “AoMeasurementQuantityis the base element that represents information on a measured physical quantity (like force.temperature,…), and so on.
Each base relation represents a link with a specific meaning between two such baseelements. E.g. AoMeasurementQuantity and AoUnit are linked together and the relation tellswhich of all possible units is the current unit of that quantity.The base model is unique for all kinds of applications that use ASAM ODS.The application model is application specific. A test system for wind tube tests may have adifferent application model than a system running engine endurance tests.The application model specifies which elements are really in use by the application. Forexample, an engine test shall measure a temperature, a pressure, and a force and will usethe Sl units Kelvin, Pascal, and Newton. These six instances are quantities going to bemeasured (thus belong to the base element AoMeasurementQuantity) or units (thus belongto the base element AoUnit). Each of them is an individual application element (derived fromthe corresponding base element), and there is a relation between each such quantity usedand an appropriate unit.