NoSQL and SQL Data Modeling: Bringing Together Data, Semantics, and Software by Hills Ted

Author:Hills, Ted [Hills, Ted]
Language: eng
Format: azw3, mobi, epub
Publisher: Technics Publications
Published: 2016-03-22T16:00:00+00:00

The representation line from the UK NINO Record Collection to UK Person Type indicates that the record collection represents the UK Person type. This means that each value of a record in the UK NINO Record Collection represents a UK Person. Since we know that the key of a UK NINO Record—the Person National Insurance Number—is always unique, we know that in fact it is the Person National Insurance Number that represents, or identifies, a UK Person.

It is not true that every NINO identifies a UK Person. It is only a NINO that has been assigned to a person, as recorded in a UK NINO Record, that identifies a UK Person. This is where the NI Number Type on the right of Figure 12-2 comes in. The NI Number Type designates the full set of NINO numbers, whether assigned or not. The full set is defined as all those strings of characters starting with two letters, then six decimal digits, and finally one suffix letter, minus certain prohibited combinations as defined by the UK Department for Work and Pensions. NINOs to be assigned to people must be drawn from this set.

Let’s look more closely at the relationship from the UK NINO Record Type to the NI Number Type. The definition of the UK NINO Record Type includes a component, the Person National Insurance Number, whose type is NI Number Type. The UK NINO Record Type incorporates the NI Number Type by aggregation; in other words, the NI Number Type is part of the UK NINO Record Type and can’t be separated from it, although it remains a recognizably separate part. The line with the solid arrowhead pointing from the UK NINO Record Type to the NI Number Type indicates this. As is standard in COMN notation, arrowheads always point in the direction of reference. The UK NINO Record Type mentions the NI Number Type, and not the other way around.

We can now see that we have two subtly different sets of values that have two different functions. The NI Number Type designates a set of strings of characters in a certain format. The UK NINO Record Collection includes a subset of all possible NI Number Type strings, specifically only those NI Number Type values actually assigned to identify persons. This subset of NI Number Type values is what represents or identifies the UK Person Type.

In striving toward our goal of efficient development of reliable systems, both the UK NINO Record Type and the NI Number Type are valuable. The NI Number Type can be used at points of data entry to ensure that character strings entered as purported NINOs are at least in the right format, whether or not they are assigned to anybody. This level of type checking is a valuable first line of defense in ensuring high data quality, and might be all that’s possible if access to the UK government’s authoritative NINO database isn’t readily available. To be really sure that a NINO identifies a UK Person, one must look in the authoritative UK NINO Record Collection to find a matching value there.

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