Addresses are one of the best examples of granularity - an address can be a single "blob" suitable for printing on envelopes, or it can be highly detailed, with every line independently accessible. The amount of detail will be a user choice, depending on the purpose to which the structure is put. However, if nothing else, the Post Code should be indexed as a means of retrieval. Consider sorting by street name and postcode - this is the index to an atlas or street directory if cross-referenced to a page number. The Post Office Address File is a very complex, and probably inaccurate, file that caters for indirect addresses such as "Lovers Lane, off Hunter's Walk, High Street, Attleborough". Also you get odd addresses such as "9 Stonor" or "By the Pond, Highgate".

The address relationship

An address is a relationship between a person or organisation and a place, usually a building. However, the relationship is one of residing at a place, or of the place’s being the residence of. People may have many residences in their lifetimes, or a place may be the residence of many people over time. So we have a many to many which resolves as a residence. Fig 1
The place has address details, which consist of address lines. Each line is part of the address. Some may be special entities in their own right, such as Town/City and Post Code. Apart from the Post Code, we can classify the address line as, say, Street, Town, County, and so on. House names and numbers may also be encapsulated in this way. So, the Residence represents something transient, with start and stop dates. A Person is more stable, unless it be someone who changes her name on marriage, or by deed poll. There may be other reasons as well. The Place has a reasonably stable “address”, but can be altered by circumstances: one case was when the property stood between two streets. The street address was that of one of the streets, because that was where the front door was. However, for some reason the front door was moved to the rear of the building, so that it “fronted” on to the other street. Thus the street address, and house number were altered unpredictably. Lulot Street in Highgate (London) is no more after the buildings were demolished. Thus a street may not have permanence, but exists for a period of time, just as Bill Jones has a life span. Each address line should have a sequence number to allow the lines to be stored and retrieved in a meaningful order.

The Address Line structure.

Each Place forms its address from a number of address lines. These need to be sequenced for retrieval and presentation. Consequently, each address line should have a sequence number to allow the lines to be stored and retrieved in a meaningful order. The other major property of an Address Line is a name, which describes it, e.g. Lovers Lane. Additionally, an “Address Line Class” may be added to distinguish between House Name or number, Town/City, County. Post Codes apply to the whole address structure, i.e. to the Place. fig 2
 

Address Purpose

An address may serve more than one purpose, e.g. as residence, place of work or business, Poste Restante and so on. This is a refinement that may not be needed by everyone. Now, could the Place represent more than one address? If it has more than one purpose, then it could. Replace the Place with a new Entity called Address, and make the Place a header. Fig 3 The link to Person is still the same. See fig. 1. If the address is a business one, the use of Person will need to be broadened to be either an individual or a Firm. This will cover Sole Traders as well as incorporporated Companies.

Post Codes

A Post Code may represent a group of dwellings, or a department in a Firm. It is a measure of delivery of mail. However, it is a useful index by which to find an address. The same place may have more than one Post Code, according to purpose. Your personal address may have a different Post Code from your business address. The Post Code entity provides validation for an entered Post Code. This means that new Post Codes need be entered prior to creating an address.

Address Line Usage

To give an address line some use as a selector, line that are Towns, Cities, or Counties may be identified and accessed by name.

Residence

Business addresses could use the Residence, since the purpose is still to link a Firm to its building. Perhaps a better name could be devised?