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# LMFDB Developers Guide

This document describes the principles behind the pages in the LMFDB, the writing style, the use of knowls, and the URLs of the home paes of mathematical objects. This document is not meant as a rigid set of rules. Rather, it is intended to help speed the creation and adoption of new material, and to help maintain a unified design as the website grows.

## Adding material to the LMFDB

Two main principles guide the development of pages.

1) New pages are developed at a workshop, through an iterative process that involves input from both experts and nonexperts. The goal is to make everyone happy.

2) The closer a page is to the top, the more scrutiny by more people is required.

A corollary of the last sentence in 1) is that a novice must be able to click their way around the site, exploring objects about which they know very little, and an expert has to be able to quickly find what they are looking for. Hence the need for 2), because only a large and diverse group will represent all the perspectives, hence the need for the first phrase in 1).

# The pages in the LMFDB

We elaborate on those four points.

## Homepages

Every object in the LMFDB has a "home page." The home page of a mathematical object is based on the idea of the home page of a mathematician, or the wikipedia article of someone famous.

An object's home page should provide a wide variety of information about the object. Basic information, of interest to both experts and non-experts, should appear near the top. More specialized information should appear near the bottom.

In the upper right corner of the home page should be the "properties" box, summarizing the most basic facts about the object. The information in the properties box should also appear in the body of the page.

Standard practice for creating the home page for a new object is to copy the template for an existing object with a good home page (elliptic curves or global number fields have been common choices) and then modify it. The Properties box and other features will already be there, and you can use them without necessarily knowing all the details of how the templates work.

Historical note: the Properties box is also known as the "Lady Gaga" box. The name comes from from John Voight's presentation at an LMFDB workshop of Lady Gaga's Wikipedia article, illustrating the value of gathering basic information in the upper-right corner of a home page.

Use knowls: Descriptions of the terminology on a home page should be put in knowls. This allows nonexperts to find basic information, without forcing experts to skim through all the documentation. The links to the knowls should be the words being defined. Don't add extraneous words like "click here".

Get feedback from both experts and nonexperts about the order in which the information appears on the home page, and the categories in which to group the material. If there is a question about whether something should go on a home page, almost always the answer is 'yes,' and you can always put it near the bottom. The main exception is when the information is not of wide interest, and it more properly belongs on the home page of a related object.

## Browse-and-search

The entry point to a mathematical object in the LMFDB is by its browse-and-search page. The upper portion of that page, that part that is visible in a typical browser when you click to the page, should contain two things:

1) At the top should be a variety of links to specific objects, and to search pages where reasonable search parameters have already been selected. The point is that a novice should be able to click around with their mouse and explore the topic, without needing to fill out a form or even know anything about the topic.

2) Below the browsing section, but still visible without scrolling, should be a search form which is suitable for use by experts.

Other material can appear in the lower portion of the browse-and-search page.

# Knowls

## Anatomy of a knowl

There are three components to a knowl:

1) Identifier. This indicates where the knowl fits into the hierarchy of information in the LMFDB, but the scheme is not as elaborate or as rigid as the URLs.

Example: ec.q.conductor

Consult with experts before introducing new first- or second-level identifiers, because it is quite tedious to alter identifiers and change all the places they are used.

2) Description (Some people think of this as the "Title" of the knowl, but titles tend to be shorter than descriptions.) This is several words that describes the knowl and helps distinguish it among knowls on similar topics.

Example: Conductor of an elliptic curve over $\Q$

(That description would be inadequate if it were any shorter.)

3) Content. This is the text that appears when someone clicks on the knowl.

As originally envisioned by Harald Schilly, knowls should contain a relatively small amount of information (because it is better to have knowls-within-knowls so the reader can determine what additional information is needed), and the content of a knowl should be context independent. This means that the information should make sense wherever it might appear.

In the example of "Conductor of an elliptic curve over $\Q$," the definitions in most textbooks may not be suitable for the content of the knowl, because the phrasing may not make sense unless the reader has just read the previous paragraphs.

Years of schooling have trained people to write in a linear fashion where each idea flows into the next. This training actually makes it difficult to write knowls. Try not to think about the specific situation in which you want to use the knowl: write something that makes sense in all the other places where other people might use it.

## Using knowls

Knowls are used in several ways:

1) To provide supplementary information (such as a definition) on a web page.

2) To provide all of the material on a web page, in a way that can easily be edited. (This is the "knowl include" option.)

3) To give details about the material only on one specific web page or a specialized set of web pages.

The above is a list of how knowls are currently used in the LMFDB. It has been suggested that the 3rd item is not the proper use of a knowl, and that there are better ways to achieve the same results.

(( more discussion is needed here ))

# URLs

One of the fundamental principles of the LMFDB is that mathematical objects should have a "home page," where we follow the analogy of the home page of a person as much as possible. Below we describe the scheme for URLs of home pages.

As much as possible, the URLs for the home pages of objects in the LMFDB should be:

1. mathematically meaningful
3. permanent
4. suitable for inclusion in a bibliography

Here and throughout this document, we say "should" instead of "must," with the understanding that some compromises will be inevitable.

Note that "unique" is not on the list of desirable properties of a URL. Multiple URLs are inevitable because part of the beauty of the subject is that the same object can arise in several ways.

Some principles:

1) If X is the URL of an object, then L/X is the URL of its standard L-function. According to the Langlands program, other L-functions associated to X have the form L(s,X,rho). Examples are

L(s,f,\sym^2)

L(s,Upsilon,\spin).

Those have URLs, respectively,

L/SymmetricPower/2/urlforf

L/spin/urlforUpsilon

2) The group comes before the field

For example, GL2/Q could occur in the URL of some object.

3) The "type of object" should come first. The following is the current list of top level URLs for home pages of objects. Note: there are other top level URLs, but these are all that currently have home pages of objects below them.

• /ArtinRepresentation
• /Character
• /EllipticCurve
• /GaloisGroup
• /L
• /LocalNumberField
• /ModularForm/
• /Motive
• /NumberField

4) "Nicknames" can be used for popular number fields.

The current list of number field nicknames is:

QsqrtN : where "N" can be a positive or negative integer. For example: Qsqrt7 or Qsqrt-5

Q : the rationals $\Q$

Qi : $\Q(\sqrt{-1})$

QzetaN : the Nth cyclotomic field

For example, Hilbert modular forms on $\GL(2)/\Q(\sqrt{5})$ could go under /ModularForm/GL2/Qsqrt5

Note that number field $\Q(\sqrt{5})$ has an "official" name as well as a nickname, so the above is not the only initial segment of a URL for those Hilbert modular forms. See the below for a a discussion of number field labels.

5) The URL of an object provides successively narrower descriptions of the object. After some number of levels (depending on the object) one is faced with the issue of naming a specific object. This final specification can be done with a label consisting of an alphanumeric string, or it can be done with a hierarchy/directory-style specification of alphanumeric strings separated by slashes (/). The specific approach should be appropriate to the object under consideration.

The following examples are currently in use, and these URLs probably should be considered "permanent", except possibly for the \<label>s:

• /ArtinRepresentation/\<dim>/\<conductor>/\<label>
• /Character/Dirichlet/\<modulus>/\<number>
• /Character/Hecke/\<number_field>/\<modulus>/\<number>
• /EllipticCurve/Q/\<label>
• /GaloisGroup/\<label>
• /LocalNumberField/\<label>
• /ModularForm/GL2/Q/holomorphic/\<label>
• /ModularForm/GL2/Q/Maass/\<label>
• /Motive/Hypergeometric/Q/\<label>
• /NumberField/\<label>

The following URL is in use but is not consistent with the above principle (at minimum, GSp should probably be GSp4 for genus 2 examples):

/ModularForm/GSp/Q/\<label>

## Some Labeling issues

Discussion is needed about \<label>s. In particular:

a) The possibility, and desirability, of consistent labels for different types of modular forms: Holomorphic, Hilbert, Bianchi, Siegel.

b) Possible new labels for number fields, if the current scheme is not suitable for Artin representations or Hecke characters. (See Issues 128 and 127 in the issue tracker.)

c) If an object naturally belongs to a Galois orbit, then the members of that orbit are given a unique (but possible arbitrary) name. The name of the Galois orbit (which typically is a letter or a string of letter if there are more than 26 Galois conjugates) is the final component of the label of the object.

Authors:
Knowl status:
• Review status: beta
• Last edited by John Jones on 2015-07-29 21:36:30
Referred to by:

Not referenced anywhere at the moment.

History: