Skip to content

Latest commit

 

History

History
386 lines (287 loc) · 18.7 KB

ATTRIBUTE_FUNCTIONS.md

File metadata and controls

386 lines (287 loc) · 18.7 KB
Raw

Attribute Functions

The conform section of a source contains, along with metadata, the address attributes and how to derive their values. The address attributes are:

  • number - the house number of an address
  • street - the street the address is on
  • unit - the apartment, suite, flat, etc of an address
  • city - the city that the address is in
  • district - one step up in the hierarchy from a city, such a county or metropolitan area
  • region - the first level administrative divisions within a country, such as state or province
  • postcode - the alphanumeric code used in many countries for sorting mail

Of these attributes, only number and street are required in a source.

In an ideal world, data sources would have a single field for each OpenAddresses conform attribute. That is, there would be a single field for number, a single field for street, and so on. Unfortunately that's rarely the case. A common occurrence is for the house number and street name to be combined into a single field, for example "123 South Main Street". To accommodate data sources like this, OpenAddresses source conforms support a number of functions to separate and join fields to create appropriate values. This page details each of the available functions and ends with a section on acceptance testing for validation.

One note, however, is that functions cannot be combined at this time. That is, a regexp function cannot be combined with a prefixed_number function to operate on a single field.

Formatting Functions

There are two functions that are specifically designed to combine two or more fields into one.

join

The join function combines any number of fields using a delimiter and is useful in cases where, for example, a complex house number is stored as two separate fields in the source data. An example of this function comes from Honolulu, HI:

"number": {
    "function": "join",
    "fields": ["HOUSEPRFX", "HOUSENUMBR"],
    "separator": "-"
}

For ease of administration, large areas of the island of Honolulu, HI are split into nine zones and each zone is split into up to nine sections. These two numbers, combined with the physical house number, create the addressable house number. Understandably, the Honolulu County GIS department stores these two fields separately but for OpenAddresses purposes, they need to be combined. For example, the source data may look like:

{
    "HOUSEPRFX": "91",
    "HOUSENUMBR": "921"
}

The addressable house number, when the join function above is applied, would be "91-921" for the address "91-921 Oaniani Street, Kapolei, HI".

Definition:

parameter value default
function join
field any field name in the data source none
separator any string of length 0 or greater a single space

format

In some instances, the join function may not be enough to handle combining several fields where two or more delimiters or hard-coded characters are required for correct value expression.

An example of the format function can be in the Netherlands:

"number": {
    "function": "format",
    "fields": ["huisnummer", "huisletter", "huisnummertoevoeging"],
    "format": "$1$2-$3"
}

The positional numeric $ format refers to the 1-based nth element in the fields array. The - is a literal hyphen.

House numbers in the Netherlands are composed of a number, an optional letter, and an optional number suffix, which are concatenated using a hyphen. Some examples of this are:

  • Ambachtsweg 4, Eede, NL
  • Rondweg 25-k143, Bladel, NL
  • Berkenring 123-m, Zundert, NL

The Netherlands GIS administration stores these three fields separately but they must be joined by the OpenAddresses source. For example, the source data may look like:

{
    "huisnummer": "25",
    "huisletter": "k",
    "huisnummertoevoeging": 143
}

The addressable house number, when the format function above is applied, would be "25-k143" for the address "Rondweg 25-k143, Bladel, NL".

One a notable behavior when using the format function is that if a referenced field has no value, it and the optional literal character values before it are not output. That is, for "Ambachtsweg 4", "4" is the huisnummer value and both huisletter and huisnummertoevoeging have no value so the $2-$3 part of the format has no effect and no literal hyphen is output.

The format parameter is required and has no default value.

Definition:

parameter value default
function format
fields an array of data source field names none
format any string referencing all elements from fields using $-positional notation

Extraction Functions

More numerous than the formatting functions are the extraction functions. These functions are used conditionally pull sections from larger values.

prefixed_number, postfixed_street, and postfixed_unit

A number of countries, namely the United States, Canada, and others, format addresses with the house number prefixing the street name and sometimes suffixed with a unit, for example, "123 South Main Street". The prefixed_number, postfixed_street, and postfixed_unit functions are for convenience to avoid the laborious and monotonous task of maintaining many copies of much more complicated regexp functions among a large number of sources. Respectively, they simply return the contiguous block of numbers from the beginning and the value after those numbers.

An example usage of this is in Asotin County, WA:

"number": {
    "function": "prefixed_number",
    "field": "address"
},
"street": {
    "function": "postfixed_street",
    "field": "address"
}

This example is very useful where a data source has very plain vanilla single "number+street" values, such as "123 Main Street" and "1220 Calle de Lago". The example data source value would be:

{
    "address": "123 Main Street"
}

prefixed_number and postfixed_street would return "123" and "Main Street" respectively.

It's quite common for a data source to contain a record that may not have a house number assigned yet (for, say, an empty lot in a new development). If prefixed_number cannot find a contiguous sequence of number prefixing a value, an empty string is returned. For example, if the data source value is "Main Street", then prefixed_number would return "", denoting no house number.

The implementations of prefixed_number and postfixed_street are very simple, they do not accommodate more complicated numbering schemes containing letters, or fractional or hyphenated house numbers, such as "143A Main Street", "15 1/2 South Maple Avenue", or "65-43 Austin St", respectively.

A source may not necessarily have to use both functions together in a conform but they commonly are.

It's also common for a single address field to contain a unit designator at the end, as in "123 Maple Street Apt 4A". In this case, postfixed_unit should be used in combination with postfixed_street to extract Apt 4A. Because postfixed_street considers the street value to be anything after the house number, it's normal to set may_contain_units to true in postfixed_street when using postfixed_unit.

postfixed_unit recognizes the following words as unit designators:

  • Unit
  • Apartment
  • Apt
  • Suite
  • Ste
  • Building
  • Bldg
  • Lot

Any text found after the unit designator is considered part of the unit. The downside of this is that if a street name legitimately contains one of these words, such as "Lindsay Lot Road", which is fortunately a fairly rare occurrence.

Definition:

prefixed_number and postfixed_unit each take a single parameter named field:

parameter value default
function prefixed_number / postfixed_unit
field any field name in the data source none (required)

postfixed_street takes two parameters: field (required) and may_contain_units (optional):

parameter value default
function prefixed_unit
field any field name in the data source none (required)
may_contain_units true or false false

remove_prefix and remove_postfix

Some data sources contain, for unknown but legitimate reasons, two fields where one prefixes or postfixes another. For example, the city of Salem, OR has two fields, ADDR_NUM and FULL_NAME, where ADDR_NUM contains the house number and FULL_NAME contains the full street address including the house number and street name.

"number": "ADDR_NUM",
"street": {
    "function": "remove_prefix",
    "field": "FULL_NAME",
    "field_to_remove": "ADDR_NUM"
}

In this example, if the FULL_NAME field value is prefixed with the ADDR_NUM field value, then the latter is removed and the remainder is assigned to the street field, otherwise the entire value found in the FULL_NAME field is used.

Here's an example data source record:

{
    "ADDR_NUM": "2130",
    "FULL_NAME": "2130 MAPLE AV NE"
}

The usage of remove_prefix above would remove the ADDR_NUM from the beginning of FULL_NAME, resulting in:

{
    "number": "2130",
    "street": "MAPLE AV NE"
}

All fields are required for remove_prefix and remove_postfix.

For a more complicated example, see Grand Forks, ND, where the addrnum field is the concatenation of house number and unit, the fulladdr field is the concatenation of house number and street, and the unit field contains only the unit number.

Definition:

parameter value default
function remove_prefix / remove_postfix
field any field name in the data source none (required)
field_to_remove any field name in the data source none (required)

regexp

The regexp function is the immensely powerful yet arcane sonic screwdriver for when no other extraction functions are an appropriate fit. Their usage is found where source data is messy or several OpenAddresses attribute values are contained in one source field.

The term "regexp" refers to regular expressions, patterns used for searching for sequences in larger pieces of text. A full tutorial on regular expressions it outside the purpose of this documentation but there are plenty available.

The regexp function needs to know which field to operate on (field) and the codified search expression (pattern). Optionally, the specific captured group to extract can be specified with replace; otherwise all captured groups are concatenated and returned.

An example of regexp usage can be found in Yolo County, California:

"number": {
    "function": "regexp",
    "field": "Address",
    "pattern": "^([0-9]+)"
},
"street": {
    "function": "regexp",
    "field": "Address",
    "pattern": "^(?:[0-9]+ )(.*)",
    "replace": "$1"
}

The pattern for number matches a contiguous block of one or more numbers from the beginning of Address and assigns to the number field whereas the pattern for street matches everything after the numbers at the beginning of Address and assigns to the street field. Here's an example data source record:

{
    "Address": "617 TUMBLEWEED TRL"
}

The application of the number and street regular expressions would result in the following:

{
    "number": "617",
    "street": "TUMBLEWEED TRL"
}

When using the replace parameter, add the positional captured groups in the desired format, with each group number prefixed with a $. For example, $1 would use the first captured group for the attribute value.

While virtually all modern regular expression flavors share identical basic behavior, there can be subtle nuances. The code that executes the regexp conform implementations is written in Python so please write regular expressions accordingly.

Definition:

parameter type value default
function string regexp
field string any field name in the data source none (required)
pattern string a compilable regular expression none (required)
replace string a string referencing 0 or more captured groups in pattern none (optional)

Compound functions

Sometimes a single conform function is not enough to correctly process a source field, but applying two or more functions would be simpler and more correct than writing a regex.

chain

The chain function allows for combining any number of conform functions as a sequence. The most common use case is when a source field contains number, street, and unit e.g. "310 WOOD ST APT 3" and "APT 3" is also listed as a separate field. Without writing a regex (which can be complex if there are many unit types), it would be impossible to extract "WOOD ST" as the street field. However, with chain, it can be easily accomplished by first extracting the street name + unit with postfixed_street and then removing the unit field using remove_postfix. Here's an example of a conform which does just that:

"number": {
    "function": "prefixed_number",
    "field": "Prop_Addr"
},
"street": {
    "function": "chain",
    "variable": "street_wip",
    "functions": [
        {
            "function": "postfixed_street",
            "field": "Prop_Addr"
        },
        {
            "function": "remove_postfix",
            "field": "street_wip",
            "field_to_remove": "Prop_Addr_Unit"
        }
    ]
},
"unit": "Prop_Addr_Unit"

The variable parameter in a chain function is a user-defined field which stores the intermediate results of the chain. In the first step in the street field example above, postfixed_street removes the house number, but the result of that computation is stored in the temporary field street_wip instead of an output field. In step 2, street_wip is referenced as the input field instead of the source field Prop_Addr. A chain function can contain any number of steps and the user-defined variable will accumulate the results of each step. The only requirement for user-specified variable names is that they should not conflict with the source fields or the standard output field names used in OpenAddresses conforms e.g. street, number, etc.

Given the following source record:

{
    "Prop_Addr": "310 WOOD ST APT 3",
    "Prop_Addr_Unit": "APT 3"
}

Applying the above conform results in the following:

{
    "number": "310",
    "street": "WOOD ST",
    "unit": "APT 3"
}

Definition:

parameter value default
function chain
variable a temporary field name to store intermediate results none (required)
functions a list of conform function definitions (which can also be chain) none (required)

Acceptance Testing

Arguably, the hardest part about defining sources correctly is making sure that the functions are configured correctly. To address this, OpenAddresses recently adopted including acceptance tests in sources to provide a test bed that serves to provide both a set of test inputs and outputs and an historical record of what data formats the source contains. Examples of acceptance tests are available for Curry County, OR and Montgomery County, TX.

Acceptance tests are entirely optional but are helpful in maintaining sources. For example, some sources, like the Czech Republic, contain highly complicated and fragile regexp patterns. The acceptance tests provide a codified justification for the complexity of the patterns so future maintainers have a base level of understanding that doesn't have to be learned the hard way. While optional, acceptance tests are recommended for all but the most trivial regexp patterns.

The test element is a child of the source root and contains the following required fields:

property type description values
enabled boolean signals the machine to run the tests true or false
description string high-level summary of the tests any string
acceptance-tests array list of tests to run

Each test in acceptance-tests contains the following required fields:

property type description values
description string summary of the test any string
inputs object map of source key -> value string->string mapping
expected object map of output attribute -> value string->string mapping, keys are conform attribute names

The machine runs the acceptance tests when enabled is set to true. As it operates on all defined attributes in the source conform, all data source fields used by the source conform must be defined in inputs.

Example

The following is an example for defining tests that use regular expressions to extract a number and street from an input field named address where the former prefixes the latter:

"test": {
  "enabled": true,
  "description": "house numbers should prefix streets",
  "acceptance-tests": [
    {
      "description": "the house number consists of only digits",
      "inputs": {
        "address": "123 Main Street"
      },
      "expected": {
        "number": "123",
        "street": "Main Street"
      }
    },
    {
      "description": "the house number can be postfixed with a letter",
      "inputs": {
        "address": "123A Main Street"
      },
      "expected": {
        "number": "123A",
        "street": "Main Street"
      }
    }
  ]
}