A table is a special tool intended for organizing the storage of structured data and access to it.
For example, information about certificates of five buildings can be presented in the form of a table from nine columns and five rows (table 22-1). Every column contains information of some character on all the buildings. Every row contains information about one building.
Row Numb. | Inventory Number | Street | Building Number | Is Municipal? | Area | Total Inhabitants | Number of Storeys | Date of Last Repair |
1 | 123 | Theatre Avenue | 12 | True | 112.2 | 12 | 2 | Oct 12, 2001 |
2 | 234 | Sea | 23 | False | 34.8 | 5 | 1 | Sept 17, 2000 |
3 | 345 | Theatre Avenue | 34 | True | 234.8 | 16 | 2 | Oct 15, 2002 |
4 | 456 | Yellow Street | 45 | True | 121.6 | 8 | 1 | Sept 1, 1999 |
5 | 567 | Theatre Avenue | 56 | False | 67 | 4 | 1 | Sept 12, 2002 |
Table 22-1. List of Building Certificates
ObjectLand allows the user to perform different operations with data organized as tables which can result in changing of individual table fields, the whole rows or columns and even creating new tables.
The system of tables in ObjectLand is a management system of relational database, that is, the database in which all the data is interpreted by the user as a set of tables.
According to the terminology of relational databases a row of the table will be called a record, a column – a table field and intersection of a row and a column – record field in the text below.
Every table field is determined by a name and type of data which will be stored in this field. For example, the field “Building Number” contains integer positive numbers, the field “Date of Last Repair” contains dates.
Maps in GDB are used for storing spatial data, tables – for storing attributive data. Several features on maps can be linked with table records. For example, every building on the city map can be linked with a record of the table “List of Building Certificates”.
In accordance with the relational model all manipulations with tables create more tables. For example, the following requests can be formulated to the table “List of Building Certificates”: “Show certificates of buildings located in Theatre Avenue” or “Show certificates of one-storeyed buildings belonging to municipal property”. When answering these requests the system forms new tables – “queries” from the main (base) table. Created tables will have the same set of fields as the base table, but only records of the base table satisfying the request will be included into them. In ObjectLand such newly created tables are called queries.
If base tables exist “on their own”, a query is a derivative from one or several base tables. It is possible to catalog a query, to be more exact, catalog the way of forming it. It means saving it in GDB. A cataloged query can always be used in further work.
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