FRED-like API interface

[epogrebnyak]

After reading https://research.stlouisfed.org/docs/api/fred/ here are some thoughts on how this app urls may look like and what they'd do.

This is fantasy url system for this app:

# dataset varname domain
# can also be 'oil', 'china', 'us'  
# the idea is to make varibale name like INDPRO short but need reference to country somewhere
/ru   # Russian macro stats     

/all - global namespace to get many variable from different sources

/domains # list all domains

# similar to FRED
# list available categories in this domain
# note in FRED categories are a graph (each id has parent id)
/ru/categories

# list all variables
/ru/names

#indicator homepage, returns an html with graph and description 
/ru/series/INDPRO


# note fred has two functions 
# one for the series info
# https://research.stlouisfed.org/docs/api/fred/series.html
# other for data
# https://research.stlouisfed.org/docs/api/fred/series_observations.html

# for the data must return something feedable to pd.read_json()

#actual data retrieved by <frequency>/<mod>, where <mod> is a mix of unit or transformation
/ru/series/INDPRO/a/yoy 
/ru/series/INDPRO/q/rog 
/ru/series/INDPRO/m/rog

# some other data 
/oil/series/BRENT/m/eop
/oil/series/BRENT/a/avg

#can we just keep it without unit sometimes? adding usd is not symmetric to eop/avg
/oil/series/BRENT/d/

# to experiment with notation - domain with underscore
/cbr_fx/series/USDRUR/d/
/cbr_fx/series/USDRUR/m/eop
/cbr_fx/series/USDRUR/y/avg

# as in https://fedstat.ru/indicator/37393
/ru_export/series/COPPER/m/vol
/ru_export/series/COPPER/m/price


#available frequencies and modifications
/cbr_fx/series/USDRUR/freq #will list a subset of h,d,w,m,q,y
/cbr_fx/series/USDRUR/mod  #will list eop, avg

#truncating data 
# reason: eg in USDRUR daily from 1991 is a lot of datapoints, may want just few latest one
# how about truncating by a year
/cbr_fx/series/USDRUR/m/eop/2017

#finalising data format - probably not a good idea - 
csv/cbr_fx/series/USDRUR/m/eop
xlsx/cbr_fx/series/USDRUR/m/eop
xls/cbr_fx/series/USDRUR/m/eop

[epogrebnyak]

In flask will need some kind of catch-all url for this

[epogrebnyak]

Possibly can formalise above as incoming json:

# per-query
format='csv' 
# good for several datapoints
domain='cbr_fx' 
# let's just accept string date stamp for start
start = '2017'

# one datapoint 
varname='USDRUR'
frequency='m' #when omitted go to highest frequency possible, usually day or month
modifier='eop'

Here modifier rog is effectively a unit of measurement and there is not default for no-modifier:

varname='INDPRO'
frequency='m' #when omitted go to highest frequency possible, usually day or month
modifier='rog'

Domain definition looks vulnerable, one domain is better for user, may use categories instead.

[epogrebnyak]

Предполагаемая единица хранения:
<НАЗВАНИЕ_ПЕРЕМЕННОЙ>-<единица_изм>-<дата>-<значение>-<частота>-<домен>

domain = 'ru'
source = 'mini-kep'
varname ='INDPRO'
unit ='rog'
frequency ='m'
date = '2017-03-31'
value = 107.1

[epogrebnyak]

@relique - does flask have a capability to catch nested URLs like /ru/series/INDPRO/q/rog

without specifiing what is after /ru/series/ or how many slashes will there be?

[relique]

Hi @epogrebnyak yes, Flask does have this capability. Sample route: @app.route('/ru/series/<path:inner_path>')

[epogrebnyak]

Reference paths, to be converted to dict/json:

/fin/series/LIBOR_3M_USD/d/2017 
/ru/series/INDPRO/a/yoy/2010
/ru/series/INDPRO/a/rog/2010 #points to the same data, 
                             #yoy and rog are the same on annual level
/ru:bank/series/PROVISION/m/eop/
/ru:bank/series/PROVISION/m/ #points to the same data, eop is default modifier
/oil/series/BRENT/a/avg/2010/2015/csv 
/ru/series/USDRUR/m/avg/2017 

domains are good to get same indicator for different countries

#CIS
ru/CPI/rog/m/2017
ua/CPI/rog/m/2017
by/CPI/rog/m/2017

#BRICS
kz/CPI/rog/m/2017
br/CPI/rog/m/2017
cn/CPI/rog/m/2017
sa/CPI/rog/m/2017

other than that they are to organise the thingking about the sources, and queries about what is availiable:

\domains #list all domains
\<domain>\series #list all variables

[epogrebnyak]

Mandatory:

• (string) domain, optionally with :subdomain
• series string
• (string) VARNAME
• (string) frequency, any letter from d, w, m, q or a.

Optional:

• (string) a postfix (unit of measurement yoy, rog, base or modifier eop, avg ), Defaults to main unit or measurement.
• (int) start year, defaults to observations start year
• (int) end year, defaults to current year
• (string) formatter - json assumed by default, may be csv, possibly xlsx

[epogrebnyak]

From catching the URL following result is needed:

domain = 'ru:bank'
varname ='INDPRO'
frequency ='m'
postfix ='rog'
start_year = None
end_year = None
formatter = None

[epogrebnyak]

I think we want an URL catcher like:

@app.route('/<string:domain>/series/<string:varname>/<path:inner_path>')

• when URL ends at domain/series/VARNAME the output is variable landing page in html
• when inner path with more slashes is specified, the output is csv/json

[epogrebnyak]

A reading on API design, to note:

• error handling
• subdomain
• doubful on versioning

[epogrebnyak]

# nominal/real + rate + info finaliser
/ru/series/GDP/a
/ru/series/GDP/a/rub/bln
/ru/series/GDP/q/rog
/ru/series/GDP/q/yoy
/ru/series/GDP/q/base

# info finaliser
/ru/series/GDP/a/info
/ru/series/GDP/q/base/info 

# seasonal adjustment
/ru/series/GDP/q/real/base/sa:<method>
/ru/series/GDP/q/real/base/nsa/info

[epogrebnyak]

А. VARIABLE NAMESPACE RULES

# Rule 0. Base URL for getting data is <domain>/series/<VARNAME>/<freq>
/ru/series/GDP/a

# Rule 1. When no postfix - fall back to default nominal time series
/ru/series/GDP/a    # will retrun bln_rub

# Rule 2. Rate of change modifiers always indicate real growth rates 
#         rog - to previous period
#         yoy - 12 month ago change 
#         and base index (some date in the past=1)
/ru/series/GDP/q/rog     
/ru/series/GDP/q/yoy
/ru/series/GDP/q/base 

# Rule 3. Aggregation postfix applies to daily observations 
#         transfomed to lower frequencies like month or year.
/ru/series/USDRUR/m/eop
/ru/series/USDRUR/m/avg

# Note. We are not adding every other transformation to API, just bare minimum. 
#       User is expected to know playng with pandas/R dataframe. 


B. TIME PERIOD

# We can optionally specifiy start and end year to truncate timeseries.
# We do not allow truncation other than by year to keep this feature simple.
/ru/series/USDRUR/m/eop/1998/2000  # 1998 to 2000, total 3 years of data 
/ru/series/USDRUR/m/eop/2017       # from start of 2017 to present


C. FINALISERS  

<expression>/csv     # get csv instead of json  
<expression>/info    # get no data, get this interpretation

D. TO IMPLEMENT: seasonal adjustment

/ru/series/GDP/q/rog/sa:<method>
/ru/series/GDP/q/rog/nsa # same as below, all time series default to nsa
/ru/series/GDP/q/rog 

[epogrebnyak]

RFC:

1. collected time series are nominal stocks/flows + prices + price indices
2. any variable except prices we can present as nominal variable = real variable * price index
3. prices are quoted at points in time (daily in our database)

Changes:

• eop, avg - applies to prices only when aggregating form daily to monthly or up.
• cannot apply eop, avg to anything other than prices