Importing Data From External EMME/2 Data Banks

Up to now, the only way to transfer data from one EMME/2 bank to another was by punching out the corresponding data in the first data bank and then reading these files back into the second data bank. Besides the fact that this way of transferring data is quite cumbersome to do, it also has some inherent drawbacks and limitations:

• Only input data can be transferred in this way, it is e.g. not possible to transfer assignment results using batch files.
• Since the data is transferred in two separate steps, it has to be stored somewhere between the two steps. In addition, the ASCII format used in the batch files usually needs more space than the internal binary representation used in the data bank -- a user may run into disk space problems, especially when transferring large matrices.
• When punching out floating point data, there is always a certain loss of information, due, firstly, to the limited number of decimals and, secondly, to the fundamental difference between representing fractional numbers in the decimal and in the binary system.
• By transferring data via batch files, the importing system only sees the sequential data file, but has no means of knowing that the data originates indeed from another valid EMME/2 data bank. Thus, it has to handle all input data as potentially containing errors and, therefore, has to do complete error checking -- which is very time consuming.

With Release 8, all the above limitations can be overcome by a new development which allows data to be transferred directly from one EMME/2 data bank to another. For this purpose, a new module 1.31, ``Import data from external data bank'', is provided. It allows opening any external EMME/2 data bank that is of the same host type as the local data bank and is accessible from the local host either as local file or as remote file accessed over a local or wide area network.

Once an external data bank is opened in module 1.31, the following data can be imported directly to the local data bank:

• All scenarios, a range of scenarios or a single scenario. Each imported scenario is transferred along with all its corresponding data, including all extra attributes and any available assignment results.
• All zone group ensembles or one particular ensemble. Each ensemble is imported including all its groups, its description and time stamp.
• All matrices of all types, a range of matrices of a given type, or one particular matrix, specified either by its number or its name.
• All functions of all classes or the functions of one particular function class.
• Auxiliary data such as demarcations, predefined windows, module parameters, switches, project title and units.

Module 1.31 always imports data sets that form a logical entity. This way, the data can be copied directly from the external to the local data bank in its binary form, without any need to reformat or restructure, and requiring only minimal consistency checks.

Any size restrictions of the local system (such as data bank dimension and licence size) apply only to the size actually used by the imported data set, but not to the dimensions that were used to define the external data bank. Thus, it is even possible to import data from an external data bank which is too large to be used with the local licence.

The following example shows how module 1.31 is used to import a matrix from an external data bank which is located on another host and accessed via a local area network:

1.31  IMPORT DATA FROM EXTERNAL DATA BANK

No external data bank opened.

Select: 1= open external data bank
        2= import data from external data bank
        3= change module parameters
        4= quit
         1

Enter: EMME/2 data bank file to be opened=\\planning\archive\base1995

External data bank: \\planning\archive\base1995
Project title:      TRUJILLO 1995 BASE YEAR DATA - EMME/2 ARCHIVE DATA BANK
    3 scenarios     200 centroids    1800 reg.nodes    4000 links
 2200 turns          30 vehicles      170 lines        6000 segments
   22 mf's           99 mo's           99 md's           99 ms's
  500 operators      50 functions     400 demarc's    40000 extras

Select: 1= open external data bank
        2= import data from external data bank
        3= change module parameters
        4= quit
         2

Select: Data to be imported
        1= network scenarios
        2= zone group ensembles
        3= matrices
        4= functions
        5= auxiliary data
         3

External data bank contains:
    10 scalar matrices (ms)
    38 origin matrices (mo)
    41 destination matrices (md)
    22 full matrices (mf)

Select: 1= import all matrices of all types
        2= import a range of matrices
        3= import a single matrix
         3

Enter: External matrix to be imported=gtr95
mf05: gtr95     observed transit demand 1995              (95-08-18 14:52)

Local matrix to hold imported matrix
Enter: Matrix( mf )= mf"gtr95"
mf09: gtr95 not initialized.
Do you want to initialize it? yes
Enter: Description (max 40 char)=observed transit demand - base year
Enter: Default value=

  1 matrices will be imported from external data bank.
OK?yes
External mf05 imported to local mf09.

  1 matrices imported.

The availability of such a powerful tool as module 1.31 to import data directly from external EMME/2 data banks will certainly have a big impact on how EMME/2 projects will be organized and data will be shared among different users in the future. Also, given the high efficiency of the direct data transfer, it now becomes possible to split large projects into several data banks which are distributed on multiple hosts, allowing several time consuming parts of the model to be executed in parallel.