Difference between revisions of "The Database API reference discovery"

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Line 191: Line 191:
 
<tr><td>F</td> <td>"farms"</td> <td>includes buildings like the Agronomy Unit</td> </tr>
 
<tr><td>F</td> <td>"farms"</td> <td>includes buildings like the Agronomy Unit</td> </tr>
 
<tr><td>H</td> <td>"hospital", the Cambridge Biomedical Campus</td> <td>the site is nonuniversity, but University premises within it are prefixed H in the usual way</td> </tr>
 
<tr><td>H</td> <td>"hospital", the Cambridge Biomedical Campus</td> <td>the site is nonuniversity, but University premises within it are prefixed H in the usual way</td> </tr>
<tr><td>K</td> <td>north city</td> <td>no site, but a number of subsites and individual buildings in the north part of Cambridge</td> </tr>
+
<tr><td>K</td> <td>north city</td> <td>no site, but several subsites and individual buildings in the north part of Cambridge</td> </tr>
<tr><td>L</td> <td>south city</td> <td>no site, but a number of subsites and individual buildings in the south part of Cambridge</td> </tr>
+
<tr><td>L</td> <td>south city</td> <td>no site, but several subsites and individual buildings in the south part of Cambridge</td> </tr>
 
<tr><td>M</td> <td>New Museums Site</td> <td></td> </tr>
 
<tr><td>M</td> <td>New Museums Site</td> <td></td> </tr>
 
<tr><td>R</td> <td>Mullard Radio Astronomy Observatory (MRAO)</td> <td></td> </tr>
 
<tr><td>R</td> <td>Mullard Radio Astronomy Observatory (MRAO)</td> <td></td> </tr>

Revision as of 18:17, 11 December 2012

This page describes how the (version 6) University Map Database API can be used to navigate among geographical objects and thereby determine relevant ref codes.

Introduction

API calls of the form

 http://map.cam.ac.uk/v6.json?ref=ref|ref|...

yield the geographical entities (buildings, sites, colleges, entrances and nonuniversity premises known to the map) with the given refs.

However, this assumes you know what the refs are.

For those buildings etc which have names, searching for them by name either with the API or the interactive map will provide the record from which its ref can be determined. But (a) colleges yield the institution not the geographical college site when looked up by name, and (b) many entities, especially entrances, do not have names at all.

Therefore, both the API and the interactive also provide the ability to look up all the subordinate geographical entities for some entity (the geographical entities are arranged in a hierarchy) using a wildcard and thereby determine related (and ultimately, if necessary, all) references. For example, using the API:

 http://map.cam.ac.uk/v6.json?ref=M*

and for the interactive map

 http://map.cam.ac.uk/?ref=M*

Geographical entity hierarchy

There are five kinds of geographical entity stored in the University Map database:

  • site (comprising university properties grouped in one physical location)
  • college (which is like a site, but refers to college properties)
  • building
  • entrance (to a building or to a site)
  • nonuniversity (selected buildings/sites useful to display and reference)

Except for nonuniversity, which stands alone, these are organised into a hierarchy.

 site/college
    |
    |----- subsite
    |        |
    |        |----- building/sub-building
    |        |        |
    |        |        |----- (building) entrance
    |        |
    |        |----- (site) entrance
    |        |
    |        |----- (staircase) entrance
    |
    |----- building/sub-building
    |        |
    |        |----- (building) entrance
    |
    |----- (site) entrance
    |
    |----- (staircase) entrance

A subsite looks just like a site, but represents a lesser group of buildings. It is not geographically contained within a site, but is linked to a parent site because of the way in which University Property Codes have historically been organised, and in the case of colleges because many colleges have separate outlying subsites.

A sub-building is just a convenient mechanism for broadening the property codes while keeping the underlying numbering scheme.

References explained

The hierarchy is reflected in the syntax of references, the codes which uniquely identify these entities. These reference codes are store along with their outlines in OpenStreetMap from which the data is obtained, using the property ("tag") ref.

References derive originally from University Estates Department property codes. These do not include college properties, so the numbering scheme has been extended to include these, and do not originally have any concept of subsites.

These property codes comprise an upper case letter which identifies a site followed by three digits identifying the building. For example M039 is the Cockcroft Building on the New Museums Site ("M"). (Estates did use an earlier numbering scheme which can be seen on the white sign boards at many entrances to the central sites. However these were abandoned in favour of this more regular scheme, and the sign boards have just not been updated).

Sometimes it is useful to represent an "Estates" building as more than one building, either because it actually is more than one (usually abutting) physical structure, or a code has been used to cover a group of not-very-distinct buildings, as in some of the farms, or it is useful to break up a large building into pieces where it is occupied in distinct parts (the Austin Robinson Building on the Sidgwick Site for example). These are represented by adding a period and another number to the reference (a decimal part, if you like). For example, the southern part of the Austin Robinson Building (the bit with the Sidgwick Buttery) is S012.3

Entrances are then represented by the building (for doors) or site (for gates etc) by the building or site code followed by a dash and one or more upper case letters. For example S012.3-A

Subsites are formed by following the site code with a slash and some more upper case letters. For example L/MATHS is the group of buildings and grounds of the Centre for Mathematical Studies.

Colleges follow the same pattern. Their codes for their main sites are their sub-domain names in upper case. For example CLARE for Clare College. Outliers are just like subsites, hence CLARE/MEM is Clare's Memorial Court property. Note that LUCY-CAV is unusual, being the only one with a dash in the code, so if you are parsing references using regular expressions, you need to allow for this.

Finally, college staircases, though individually part of particular buildings, are actually represented college-wide. Hence they are subiordinate to college sites and subsites, and their letter is separated from the site code by two dashes. Thus DOW--P is Downing's P staircase, which happens to be in the East Range though there is nothing to tell you that.

In detail

If X stands for one or more upper case letters, nnn for three digits and n for digits in general,

sites/colleges:  X  
subsites:  X/X  
site and subsite entrances:  X-X  X/X-X  
buildings:  Xnnn  X/Xnnn  
sub-buildings:  Xnnn.n  X/Xnnn.n  
building entrances:  Xnnn-X  Xnnn.n-X  X/Xnnn.n-X  X/Xnnn.n-X  
college staircases:  X--X  X/X--X  

Reference browser

For casual use to determine a reference, and for illustration of the API, a live reference hierarchy browser is under construction. This will be at

 http://map.cam.ac.uk/help/refbrowser/

This uses exactly the API wildcard requests as shown below.

Wildcards

You can ask for the descendants of a referenced item using an asterisk as a wildcard in place of the relevant piece of the reference.

There can only be one wildcard per ref. Also, it is not a general regular expression: a wildcard matches the whole of one piece, i.e. X, nnn or n above.

A single asterisk provides a starting point in the absence of any other, providing all the top-level sites and colleges, thus (using the API):

 http://map.cam.ac.uk/v6.json?ref=*

Given a particular site, CLARE say (obtained from the result of the above) one can then obtain all its subsites (if any), thus:

 http://map.cam.ac.uk/v6.json?ref=CLARE/*

Note that buildings of a site or subsite yields sub-buildings as well, because they aren't actually subdivisions, thus:

 http://map.cam.ac.uk/v6.json?ref=S*

includes S031.3 (as in the example above). However, one can also obtain the sub-buildings of a building code even if the building that would be represented with that code does not actually exist. Hence:

 http://map.cam.ac.uk/v6.json?ref=S031.*

This is useful in circumstances where you have the original property code but don't know whether it is divided up or not in the map. This will be useful in those circumstances.

 http://map.cam.ac.uk/v6.json?ref=SO31%7CS031.*

All the staircases at Clare College (main site only):

 http://map.cam.ac.uk/v6.json?ref=CLARE--*

and at Memorial Court:

 http://map.cam.ac.uk/v6.json?ref=CLARE/MEM--*

Results

The results from wildcard requests are just like those for any other request, namely an array of JSON objects, each representing the properties of the items yielded. Of particular note for geographic entities is their full reference and their location as latitude and longitude. Complete details are shown in the main main API documentation.

However, results for wildcarded references are excerpted entities, that is they do not contain full details of further hierarchy, such as occupants of buildings. Omitted elements for excerpts are listed with an asterisk in the main API documentation.

Combining patterns

As with non-wildcard references, several can be requested at once, separating them with a vertical bar. Therefore, all entrances of both M031.1, M031.2 and M031.3 can be obtained thus:

 http://map.cam.ac.uk/v6.json?ref=M031.1-*%7CM031.2-*%7CM031.3-*

Note that you can't use ref=M031.*-* as you can only have one wildcard per reference.

Non university premises

In general, non-university premises do not have standard University property codes, for obvious reasons. They may not even have ref tags in OpenStreetMap. Therefore their "reference" is more general, comprising the name of the operator of the premises, followed by a colon, followed the the 'ref' if there is one or the building or site name (which may be the same as the operator name) if not. For example:

 Arbury Road Baptist Church:Arbury Road Baptist Church
 Anglia Ruskin University:Anglia Ruskin University (Cambridge Campus)

No particular distinction is made between sites and buildings for non-university properties in the record returned (though they are drawn differently on the map).

There are a few buildings operated by non-university organisations which do actually have University property codes (usually because they are leased from the University). Hence MRC-CBU occupies:

 Medical Research Council:L050

In this case, note that all its entrances can be obtained with

 http://map.cam.ac.uk/v6.json?ref=L050-*

not including the "Medical Research Council:" part.

Other starting points

As well as listing everything from the top or searching by name to obtain a reference, there are three other options if you don't know a reference:

  • When you ask for institutions, their locations and (main) entrances (both provided in the address info elements) contain references to the buildings and/or sites they occupy and the main entrances to get there. These can be followed up with a ref query to obtain more detail or a wildcard ref query to obtain subordinates.
  • By bounding box. Using a 'bb' query, one can obtain all institutions within an area, and these can be filtered by institution class as in filter=academic|nonacademic. However, it is also possible to use filters for site (which includes college sites, as opposed to college institutions, and includes subsites), building and entrance within an area. When qualify with any of these, institutions are not also returned unless you also explicitly filter for them. Thus filter=building only yields buildings. The centroid of buildings and sites must lie within the bounding box for them to be located, except that when requesting sites, if any main entrance falls within the box, the site is found. Thus, the following example provides all of the buildings in and around the New Museums Site:
 http://map.cam.ac.uk/v6.json?bb=52.2021,0.1184,52.2047,0.1218&filter=building
  • For college staircases, you can guess! The college code is its upper case sub domain and the staircase letter is used in the reference code. So if you want staircase P in Downing, it is easy to ask for ref=DOW--P

Reference table

The following table also lists the main top-level codes, for reference. However, don't rely on this for a complete set, as new ones may be added.

code description notes
A Old Schools area there is no site 'A' but the buildings in this area are coded Annn
B Silver Street/Mill Lane Site
C Scroope Terrace area there is no site 'C' but the buildings in this area are coded Cnnn and there are several subsites C/X
CUP Cambridge University Press CUP is treated as part of the University for the purposes of the map
D Downing Site
E Old Addenbrooke's Site
F "farms" includes buildings like the Agronomy Unit
H "hospital", the Cambridge Biomedical Campus the site is nonuniversity, but University premises within it are prefixed H in the usual way
K north city no site, but several subsites and individual buildings in the north part of Cambridge
L south city no site, but several subsites and individual buildings in the south part of Cambridge
M New Museums Site
R Mullard Radio Astronomy Observatory (MRAO)
S Sidgwick Site as well as the site, there are numerous outlying buildings to the west of Cambridge prefixed with S and a number of subsites
T Madingley Rise Site
W West Cambridge Site
The colleges
CAI Gonville & Caius College
CATHS St Catharine's College
CHRISTS Christ's College
CHU Churchill College
CLARE Clare College
CLAREHALL Clare Hall
CORPUS Corpus Christi College
DAR Darwin College
DOW Downing College
EMMA Emmanuel College
FITZ Fitzwilliam College
GIRTON Girton College
HOMERTON Homerton College
HUGHES Hughes Hall
JESUS Jesus College
JOH St John's College
KINGS King's College
LUCY-CAV Lucy Cavendish College
MAGD Magdalene College
MURRAYEDWARDS   Murray Edwards College
NEWN Newnham College
PEM Pembroke College
PET Peterhouse
QUEENS Queens' College
ROBINSON Robinson College
SEL Selwyn College
SID Sidney Sussex College
STEDMUNDS St Edmund's College
TRIN Trinity College
TRINH Trinity Hall
WOLFSON Wolfson College