Chronological Query Language (CQL)

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The Chronological Query Language (CQL) is a tool for formally describing chronological models (Bronk Ramsey 1998). It is most commonly used to input data for Bayesian radiocarbon calibration in OxCal (Bronk Ramsey 2009). stratigraphr includes an R interface for CQL2, the version used in OxCal v3+.

Overview

Individual CQL commands (see https://c14.arch.ox.ac.uk/oxcalhelp/hlp_commands.html) are implemented as cql_* functions.
Use cql() to group together CQL functions or include arbitrary CQL code.
Execute CQL scripts in OxCal using write_oxcal() or the oxcAAR package.

Writing CQL models

library("stratigraphr")

Generating CQL models from other types of data

Used in the simple way above, stratigraphr’s CQL interface offers little benefit over writing CQL directly. Its real power is in combining cql() with other R tools to build models based on other data.

For the following examples, we will use a simple example dataset of radiocarbon dates:

library("purrr")
library("dplyr")
#> 
#> Attaching package: 'dplyr'
#> The following objects are masked from 'package:stats':
#> 
#>     filter, lag
#> The following objects are masked from 'package:base':
#> 
#>     intersect, setdiff, setequal, union

dates <- data.frame(
  lab_id = c("ABC-001", "ABC-002", "ABC-003", "ABC-004", "ABC-005"),
  age = c(5050, 5000, 4950, 4900, 4850),
  error = c(30, 30, 30, 30, 30),
  phase = c("Phase 1", "Phase 1", "Phase 1", "Phase 2", "Phase 2")
)

Tabular data

With radiocarbon data in a tabular format, you can take advantage of dplyr’s powerful tools for data manipulation to build CQL models programmatically.

For example, use dplyr::mutate() to concisely express a table of dates as CQL R_Date commands:

dates |>
  mutate(r_date = cql_r_date(lab_id, age, error)) |>
  pluck("r_date") |>
  cql()
#>  // CQL2 generated by stratigraphr v0.5.0
#>  R_Date("ABC-001", 5050, 30);
#>  R_Date("ABC-002", 5000, 30);
#>  R_Date("ABC-003", 4950, 30);
#>  R_Date("ABC-004", 4900, 30);
#>  R_Date("ABC-005", 4850, 30);

Or use dplyr::group_by() and dplyr::summarise() to build phase models. This is a three stage process:

Preprocess the dates, e.g. to order phases.
Group dates by phase and summarise them with cql_phase().
Group phases into a sequence, using boundaries to automatically add boundary constraints between them.

dates |>
  group_by(phase) |>
  summarise(cql = cql_phase(phase, cql_r_date(lab_id, age, error))) |>
  arrange(desc(phase)) |>
  summarise(cql = cql_sequence("Example Sequence", cql, boundaries = TRUE)) |>
  pluck("cql") |>
  cql() ->
  example_cql

example_cql
#>  // CQL2 generated by stratigraphr v0.5.0
#>  Sequence("Example Sequence")
#>  {
#>   Boundary("");
#>   Phase("Phase 2")
#>   {
#>    R_Date("ABC-004", 4900, 30);
#>    R_Date("ABC-005", 4850, 30);
#>   };
#>   Boundary("");
#>   Phase("Phase 1")
#>   {
#>    R_Date("ABC-001", 5050, 30);
#>    R_Date("ABC-002", 5000, 30);
#>    R_Date("ABC-003", 4950, 30);
#>   };
#>   Boundary("");
#>  };

Stratigraphs

…

Running CQL models

You can run models generated by cql() using the desktop or online versions of OxCal by simply copying the output into the program. Alternatively, use write_oxcal() to create a .oxcal file:

oxcal_cql <- cql(
  cql_r_date("ABC-001", 9100, 30),
  cql_r_date("ABC-002", 9200, 30),
  cql_r_date("ABC-003", 9300, 30)
)

write_oxcal(oxcal_cql, "cql.oxcal")

You can also run OxCal directly through R using the oxcAAR package. This depends on a local installation of OxCal. If you already have one installed, you can set the path to the executable using oxcAAR::setOxcalExecutablePath(). Otherwise, use oxcAAR::quickSetupOxcal() to download one, for example to a temporary directory:

library("oxcAAR")
quickSetupOxcal(path = tempdir())

You can then use oxcAAR::executeOxcalScript() to run the CQL script and oxcAAR::readOxcalOutput() to read the output back into R.

executeOxcalScript(oxcal_cql) |>
  readOxcalOutput() ->
  oxcal_output

You can parse the output with oxcAAR::parseOxcalOutput() and visualise it using oxcAAR’s built-in plotting functions:

oxcal_parsed <- oxcAAR::parseOxcalOutput(oxcal_output)
plot(oxcal_parsed)
calcurve_plot(oxcal_parsed)

The current CRAN version of oxcAAR (v. 1.0.0) does not read the posterior probabilities produced by a model with Bayesian calibration, so to work with these you need to install the latest development version (devtools::install_github("ISAAKiel/oxcAAR")). With this, oxcAAR::parseOxcalOutput() also contains the modelled results in $posterior_sigma_ranges and $posterior_probabilities. Again, you can quickly visualise these with the built-in plotting functions:

# Not run: slow
example_oxcal <- executeOxcalScript(example_cql)
readOxcalOutput(example_oxcal) |>
  parseOxcalOutput() |>
  plot()

References

Bronk Ramsey, Christopher. 1998. “Probability and Dating.” Radiocarbon 40 (1): 461–74.

———. 2009. “Bayesian Analysis of Radiocarbon Dates.” Radiocarbon 51 (1): 337–60. https://doi.org/10.1017/S0033822200033865.

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