Structuring Data Dictionary Files
Before a table can be loaded into the database, a data dictionary (DD) must be created telling the database how to handle each column. The user may create a data dictionary themselves (either manually or using the "ddgen" program), or they can simply provide the Exoplanet Archive with enough information to create a proper DD for them.
Data Dictionary Columns
| Name | Description | Examples |
| cntr | Ordinal number of the column | 1, 2, 3, etc |
| name | Name of the column as it will appear in the database | (usually the same as originalname) |
| originalname | The original name of the column extracted from the input table. | ra, fname |
| description | Description of the column (character string) | "Degrees from the moon" |
| units | Physical units of the column values. | arcsec, hours, deg, Jansky |
| intype | Data type of the columns in the input ASCII file. Possible types include int, double, float, char, decimal, and date. | int, double, char, date |
| format | The format of data output from the database is by default identical to the format in which they are stored in the database. Users occasionally require custom output formats for presentation. This field allows such customization (uses C language data formatting standard). Ordinarily left blank. | %19s %5.3f %14d %.2f %0d |
| dbtype | The specific data type as stored in the database (i.e.,
integer, date, etc). Some data types, like decimal and
character, require additional information specifying the
lengths of the string, for instance:where XXX denotes the length of a character string, YY is the number of digits before a decimal point, and ZZ is the number of digits following the decimal. |
decimal(17,16) double float character(20) date |
| nulls | Boolean value that specifies whether nulls are allowed in this column | y or n (default is y) |
| indx | Indicates whether a column will be indexed in the database to improve query speed. The value of this parameter can be "n" or "y". Data providers should not modify this field; it will be updated by IRSA if that column is indexed. | y or n (n is default) |
| tablFlg | This parameter determines when the column appears in the query form. It may appear only in the short form ("0"), long form ("1"), or always appear ("2"). Tables that have many columns (e.g., the 2MASS XSC), are often more convenient to the user if they are separated into short (the most important or useful columns) and long (everything) forms. | 0, 1, or 2 (default is 2) |
| groupID | The groupid is, by default, the value of the column index
counter. If you want to "attach" certain columns to other
columns, use the groupid index to attach the column to a
specific index value.
EXAMPLE: Suppose you have a column named "j_m" that corresponds to the J-band magnitude, with an index value equal to 10 and group ID equal to 10. Now suppose there is an associated error uncertainty, "j_msig" that has an index value equal to 11 and group ID equal to 11. To group these two columns together, set the group ID of j_msig to 10, thereby attaching this column to the column with index cntr equal to 10. This way, "j_msig" is always written to the output table along with "j_m." |
1, 2, etc (default is this column's cntr) |
| tblid | Included for possible expansion. Leave blank. | |
| nnulls | Included for possible expansion. Leave blank. | |
| minimum | Included for possible expansion. Leave blank. | |
| maximum | Included for possible expansion. Leave blank. | |
| mean | Included for possible expansion. Leave blank. | |
| stddev | Included for possible expansion. Leave blank. | |
| sel | This boolean determines the selection status of the column. Three values are possible: "y" (yes), "n" (no), or "h" (hidden). If yes, the column is automatically selected (that is, by default the column will appear in the output table). If no, the column will not appear in the output table. If hidden, the column will not appear in the query page (i.e., it is hidden from the user). | y, n, h |
| notes | Additional notes describing the column. You may enter text or a URL link (to documentation, for example). |
Data Dictionary Headers
| Name | Description |
| fixlen | "T" refers to a fixed-length IPAC tables. "F" is non-fixed, and consequently is read sequentially. |
| alias | To "Alias" or associate a column with a character string. This parameter is usually set to "none." |
| primary | Primary key column. If "none", the default is "cntr" |
| spt_ind | The column name containing the spatial index |
| longitude, latitude | The column names containing ra and dec |
| x, y, z | Column names of the x, y, z spatial coordinates |
Sample Data Dictionary
The data dictionary file 2MASS_LGA_IRSA.24808.dd corresponds to this input table from the 2MASS Large Galaxy Atlas: 2MASS_LGA_IRSA.tbl.See the Tutorial for more information on how to generate a DD file.
